->''"Light-years isn't time! It measures distance!"''
-->-- '''Boy in Brock's Gym''', ''VideoGame/PokemonRedAndBlue''

Many times when a measurement is given, the units of measurement don't make sense for what is being measured. This is especially annoying when the character suffering from UnitConfusion is supposed to be a scientific genius.

This occurs frequently in ScienceFiction. Compare SciFiWritersHaveNoSenseOfScale. Averted when the writers use FantasticMeasurementSystem, as the writers can redefine time units whenever they like. If they care to keep it in mind.
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!!Examples

[[foldercontrol]]

[[folder:General]]
* A frequent instance of Unit Confusion is when "watts" is used with a unit of time, as in "watts per second". "Watts" already incorporates a rate (one watt = one joule per second) so "watts per second" only makes sense if referring to a power source that is changing in intensity. A similar mistake is the use of "watts" when it is really a quantity of energy that is meant, as in "this battery can store up to 200 megawatts of power", when the accurate thing would be to measure the stored energy in joules (watt-seconds), watt-hours (1 Wh = 3600 J), or as technicians usually do, in ampere-hours (which when multiplied by the battery's voltage give watt-hours).
* A mistake that seems to be getting less common (but it still showed up in, eg., ''Series/{{Earth 2}}''): Like parsecs, light-years are a unit of distance (the distance light travels in a year), not time. Whether or not the phrase "light-years more advanced" is a mistake or just an analogy (as in "miles ahead") is debatable, and probably varies from case to case.
** People mistook "light-years" to be a construction along the lines of "[[CallARabbitASmeerp Space Miles]]" or "[[TwoOfYourEarthMinutes Earth Minutes]]" - sciencey word + unit of measure = sci-fi unit of measure.
*** Of course due to the effects of [[http://en.wikipedia.org/wiki/Time_dialation time dilation]] light does not feel the passage of time so in the incorrect interpretation a light-year is no time at all.
** To increase the confusion a bit more, the second in parsec (parallax second) is a unit of angle (an ''arc''second), while the year in light-year is indeed a unit of time.
* One obscure enough that it comes up all the time: Since 1968, the standard unit of absolute temperature is "kelvins", not "degrees Kelvin". The older usage dates to before the 13th General Conference on Weights and Measures (CGPM).
* On a related note, some works make reference to a temperature which is lower than absolute zero. Absolute zero occurs in the total absence of heat or energy of any kind. You can't get colder than that.
** Another related fallacy is the assumption that, for example, [[OvenLogic 40°C is twice as hot as 20°C]]. This is not true because 20°C is equal to 293.15K; twice as hot as this would be a lot more than 313.15°C (though not as much more as you might think; the relationship between heat and temperature is exponential rather than linear).
** Technically, negative absolute temperatures ''do'' exist, but these are only mathematical abstractions describing a very particular states of matter, such as the excited electrons in the laser's working medium, and they don't refer any actual temperature.
*** What's more, negative temperatures are actually considered ''hotter'' than positive temperatures.
* Perhaps not, strictly speaking, a unit, but "AD", unlike "BC" and "CE", is supposed to come ''before'' the year, so "2005 AD" is incorrect. This particular error is so near-universal both in and out of television that it's even accepted (and used) by professional historians.
** Another frequent confusion with casual users of A.D. comes from the (incorrect) notion that it stands for "After Death." Their thinking is that years B.C. were years before Christ was born, and years A.D. were years after Christ died, with 30-some-odd years passing in between that weren't numbered. In reality, A.D. stands for ''Anno Domini'' ("in the year of our Lord") and was supposed to mark the year that Christ was ''born'', so the day after 31-December-1 B.C. was 1-January-A.D. 1. Note that there is no year 0, and due to old calculation errors, historians now believe that Jesus was born in the single digits B.C. (but it's easier to change one date and live with the oddness than to change all of them to recalibrate the timeline).
*** Some astronomers use a year zero to facilitate calculations between years (namely, subtraction). This is also why you'll see years given as negative numbers. It's much easier to do math by hand or by programming if you don't have to make strange exceptions for how numbers work at any given point, and then just convert (say) -752 to [[UsefulNotes/TheRomanRepublic 753 B.C.]]
*** Other astronomers use a Julian Day Number to describe dates, and that has no "year" component at all.
* Confusion between metric units and AmericanCustomaryMeasurements occurs all too often, in TV and in real life, where a person accustomed to using one may not realize that a foreigner is giving them numbers in meters rather than feet.
** In TV, HilarityEnsues. An example from ''LastOfTheSummerWine'' involves Wesley assuming the pretentious Seymour used metres rather than feet in his design for a kite, with the result being the size of a hang glider.
** In real life, it [[http://www.cracked.com/article_16521_p2.html causes Mars Climate Orbiters to disappear]], or [[http://en.wikipedia.org/wiki/Gimli_Glider planes to run out of fuel half-way through their scheduled trip]].
* Confusion between Imperial and American Customary measurements is common as well. The two share the names of measurements, and lengths are the same value in both, but not volumes - pints and gallons for example. (An Imperial pint is 20 Imperial fluid ounces; a U.S. liquid pint is 16 U.S. fluid ounces. Similarly, a U.S. ton or "short ton" is exactly 2000 pounds, but an Imperial ton or "long ton" is 2240 pounds -- because it's exactly 160 stone.)
* Occasionally, confusion between normal ("avoirdupois") ounces and Troy ounces can occur. Gold, silver, and other precious metals are still traded in units of Troy ounces; a bullion ingot of exactly 1 Troy ounce would weigh 1.07 ounces on a postal scale.
* In relativistic calculations, the speed of light is often set to the unitless number 1, as this simplifies equations (for example, E=mc[[superscript:2]] becomes E=m). This makes time and space use the same units, so that a light-year actually does measure time as well as space (it's equivalent to one year). It's doubtful that this justifies any of the other examples on this page.
** One of the major, earth-shattering revelations of relativity was that spatial and temporal dimensions are, in some sense, the "same thing". One can, in fact, use units of time and distance interchangeably, and be correct -- i.e. you can talk about "years of distance" or "kilometers of time" and be technically correct. If you work with relativity a lot, you'll get pretty used to using just "year" as a unit of distance -- which is perfectly correct.
** You could also use distances to measure time -- which isn't commonly done, because a kilometer of time, for example, is a very small amount of time -- around about 1/300,000 of a second. But "kilometers of time" are seen in long-distance telecommunications, where signals take noticeable time to propagate, and even "millimeters of time" become important in designing circuits that switch billions of times per second, such as those in a modern CPU.
** With some mucking around with unit conversions it is possible to measure ''mass'' in units of distance. Starting from kilograms, multiply by G (the gravitational constant) then divide by c[[superscript:2]]. This leaves you with your mass in meters, which will be very small (the Earth's mass is about 9 millimeters).
*** Incidentally, this is the formula for a Schwarzchild radius (i.e. where a black hole's event horizon is). So a black hole with a mass equal to Earth's would be 9 mm in radius, or 18 mm across. As a quick approximation, a black hole's radius is 3 km for every Solar mass it has. A theoretical black hole with a mass equal to the mass of the observable universe would have a radius about equal to the radius of the observable universe (black holes become progressively less dense as they become heavier).
* The confusion regarding storage space. To a computer, a kilobyte is 1024 bytes, a megabyte is 1024 kilobytes, a gigabyte is 1024 megabytes and so on. However, to hard drive manufacturers, a kilobyte is 1000 bytes, a megabyte is 1000 kilobytes, etc. To avoid confusion in recent times, the [[http://en.wikipedia.org/wiki/Binary_prefix binary prefix]] system was invented. So a kibibyte is 1024 bytes and a kilobyte is 1000 bytes. Still, the old way is interchangeable.
** Mac OS X Snow Leopard and recent versions of Ubuntu report space with each order of magnitude increasing every 1000.
** The old High Density 3.5-inch floppy disks were marketed as being "1.44 MB". Their actual storage capacity (before formatting) was neither 1.44 x 1000 x 1000 bytes, ''nor'' 1.44 x 1024 x 1024. It was 1.44 x 1000 x 1024 bytes, or 1440 Kilobytes.
** Hard drive manufacturers most often use the convention of one billion bytes to the gigabyte to make their products' capacities sound bigger. Even flash memory chips, which are manufactured in powers of 2, report their size in powers of 10 so that they can use the extra 5% to 7% as spares in case sectors of the chip wear out.
** "Kilo" and "Mega" are exactly 1000 and one million, respectively, when describing data transfer rates in ''bits'' per second; e.g. a 56 kbps analog modem transfers data at 56,000 bits per second, ''not'' 57,344 (56 x 1024) bits per second. However, the number of kilo''bytes'' transferred per second is in increments of 1024 bytes, to match the numbers reported by the file system.
* Many writers have trouble understanding the proper usage of units of distance, area and volume. You cannot have, for example, "a one square mile radius". It's describing an area, yes, but it's still a "one mile radius", and also an area a fair bit bigger than one square mile.
* The hectare is not a unit of distance, but a unit of area equal to that of a square whose sides are 100 meters long, i.e. 10,000 square meters.
* Inverted with some obfuscated measurements like the becquerels per diopter, which is just a roundabout way to describe meters per second.[[note]]The becquerel measures frequency, with ''n'' becquerel meaning "''n'' per second", while the diopter is used for lenses, with a ''n'' diopter focusing parallel light rays 1/''n'' meters away from it. Technically, that means "becquerel per diopter" is "(1/s) per (1/m)", or m/s.[[/note]]
[[/folder]]

[[folder:Anime and Manga]]
* The first English dub of ''DragonBallZ'' falls victim to this trope: When Bulma is explaining to the group why traveling to Namek would be impossible, she gives her answer in years, then promptly adds "And that's in light-years!" [[HandWave Perhaps]] Bulma is distinguishing years in an ordinary slower-than-light craft from years at ''c''.
* In ''Manga/{{Bleach}}'', Ryuken Ishida tells his injured son that if he yell 5 Hertz louder he'll reopen his wounds (basically telling him to shut up), but Hertz is a measure of frequency (high or low) not intensity (decibels in the case of sound). But then Uryu ''is'' kind of a GlassCannon, [[{{Pun}} so to speak]], and the area around a wound may have a [[GlassShatteringSound resonant frequency]] that [[HandWave he almost hit]].
* Anime/{{Pokemon}} also makes the same Hertz/decibels mistake in an episode centered around Marill. This is especially egregious as the person making the mistake is supposedly an expert on this sort of thing; yet Marill had previously appeared in the series without the error being made.
* In ''[[LightNovel/DirtyPair The Dirty Pair]]'' original TV series episode ''Lots of Danger, Lots of Decoys'', the bomb Kei plants in the [[FakinMacGuffin decoy container]] counts down in metric time; i.e. 2:99:99.
* Lampshaded in ''Anime/DokiDokiPrecure'''s [[EndingTheme ending]] DancingTheme, "Kono Sora no Mukou".
-->No matter how many lightyears away it is, the future is not far off!
-->Of course I’m well aware it’s not a unit of time
[[/folder]]

[[folder:Comics]]
* Parodied/subverted in a ''FoxTrot'' strip: Jason is playing a racing videogame while his mother is trying to get him to come to dinner. Jason, who had earlier said "Just a sec," clarifies that he meant a ''parsec''; just until he ''drove an entire parsec in the game'', which would take him over 10 million years.
** Another time, Jason decided to take up baking, and mused over whether the 350 degrees he had to set the oven at were in Celsius, Fahrenheit, or kelvins.[[note]]For the record, 350 degrees Fahrenheit is a moderate oven temperature, 350 degrees Celsius is much higher than most ovens can go, and 350 kelvins isn't even hot enough to boil water.[[/note]] Peter sarcastically suggested that he rotate the oven almost a full circle. [[DontBeRidiculous "Don't be silly, Peter."]]
* Parodied in ''ComicStrip/{{Frazz}}'', when Caulfield points out rather loudly that light-years are a measure of distance. The teacher then tells him to quiet down because he's "making a ton of noise."
* A ''{{Mafalda}}'' strip had a teacher giving her students a math word problem where they had to calculate the area of a field measuring X by Y ''hectares''. Amusingly enough, a later compilation featured an entire page of sketches by the author mocking himself for the mistake (the best is one where Susanita says "Hey Quino, you big idiot! How many liters are there in a kilometer?")
* [[http://www.politedissent.com/index.php?s=pico&submit=search This]] ''Invincible ComicBook/IronMan'' panel gets the unit type right but ''royally'' screws up the SI prefix: a "picobyte" would be one ''trillionth of a byte''. Must be ''really'' optimized code. Osborn probably meant to say "petabyte" or 2^50 bytes.
* In the Dutch comic "Heinz", the eponymous character asks what a light-year is, and the specialist responds that it is a year in which everything goes off without a hitch. This might be more of a malapropism, though.
* ScroogeMcDuck has often boasted of his money bin storing "three cubic acres" of cash. An acre, of course, is a two-dimensional shape, and cubing it would create a geometrically-impossible ''six-dimensional'' shape. Although that would go a long way towards explaining just how all those countless billions fit inside that single building. [[labelnote:handwave]]Carl Barks could have meant that Scrooge's money bin consisted of three enormous cubes of cash, roughly 64 m on a side, which would give each side of said cube an area of one acre.[[/labelnote]]
* In a book of ''TheScrameustache'', one Galaxian captain orders to reduce the speed by 2 parsecs. Perhaps it was short for "2 parsecs per year," the way someone going 25 m.p.h. might say "reduce our speed by 2 miles."
[[/folder]]

[[folder:Fan Fiction]]
* In ''Fanfic/ThePrayerWarriors Threat of Satanic Commonism'', Benry sells 2,000 kilograms of drugs to Rika and Books for $10 per kilogram, which is quite cheap. Books then leaves with the 2,000 kg of drugs (over 4,000 pounds) too quickly for [[PercyJackson Grover]] to shoot him with a sniper rifle.
[[/folder]]

[[folder:Films]]
* The most famous example of all: Han Solo bragging that his ship can make the Kessel Run in "less than twelve parsecs". Parsecs are a unit of distance, not time. While this has been {{Retcon}}-ned to death with constantly shifting backstories about skilled pilots shaving distance by flying close to black holes, even those omit that the parallax second is based on local (terrestrial) factors, specifically the radius of the Earth's orbit, [[TranslationConvention and would have no meaning in "a galaxy far, far away"]], though it is possible they are using a different planet's parallax second.
** Though even George Lucas seems to have forgotten this (see next bullet point), this error seems to have been intentional and meant to paint Han as a blowhard. Not only does the script pretty much say so (and earlier drafts more so), but if you watch the scene closely, Ben kind of rolls his eyes, seeing through Han's BS.
** Another explanation offered was that the Kessel Run was between multiple points that were moving apart from each other, starting from Kessel. The implication was that to visit each point with a total traveled distance of only twelve parsecs was quite fast indeed.
*** To further confuse the issue, J.W. Rinzler's 'The Making Of Star Wars' makes the claim that a "par-sec is a navigational calculation, not a measurement of time; that is, the ship is fast because it's smart."
** In a rather literal meta-example of this trope, there was much confusion over the definition of the term "unit" from ''AttackOfTheClones'' (referring to the two hundred thousand units being ready and a million more well on the way). Many assumed it referred to a military unit, and [[FlameWar took issue]] when it turned out to refer to [[SciFiWritersHaveNoSenseOfScale an individual clone]]. The thing is, it had always referred to an individual clone, even before the movie came out as the ''AttackOfTheClones'' movie novelization (which came out about a month before the movie did) [[AllThereInTheManual pretty much told us that "unit" referred to a unit of production]], and matched the "million more well on the way" statement with "a million clone warriors".
* In ''Film/Plan9FromOuterSpace'', one of the aliens says "Foolish humans, we have had space travel for eons of your light-years." An aeon being one billion years and a light-year being a measure of distance... (Then again, this is the same alien who said that "A ray of sunlight is made up of many atoms.")
* Used intentionally as a major plot point in ''ThisIsSpinalTap''. While trying to work out a big, stadium-pleasing onstage stunt to help the show, Nigel draws plans for a Stonehenge monument on a diner napkin, and the monument is built to the exact specifications he wrote, 18 ''inches'' (18"), not 18 feet (18'). This leads to "a Stonehenge monument on the stage that was in danger of being crushed by a dwarf."
* In the movie ''{{Stealth}}'', the processing speed of the AI was given in "terabits per second". This is not a unit of processing speed, but throughput. Processing speed would probably be measured in MIPS (millions of instructions per second) or flops (floating point operations per second), though the processing speed needed to keep up with I/O rates in the Tbps would still have to be impressive.
* In ''Film/IronMan1,'' Tony Stark tells Yinsen that his mini arc reactor has a power output of 3.2 gigajoules per second (i.e. 3.2 gigawatts). Yinsen says that it could power his heart for a thousand lifetimes, and Tony responds, "Or something big for 15 minutes". Gigawatt is a measurement of ''power,'' not potential energy, so Yinsen shouldn't know that. Tony may have decided it wasn't important enough to correct him.
* In the second ''Film/{{Taxi}}'' film a policeman's French dialogue indicates that the protagonist's souped-up taxi was traveling at '200 kilomètre à l'heure'. In the English subtitles this is [[BlindIdiotTranslation blindly translated]] as '200 miles an hour'. It has no bearing on the plot but it credits the vehicle as going much faster than it really is.
[[/folder]]

[[folder:Literature]]
* Often times Creator/JulesVerne' books contained measurements and spot on calculations. However, when they were brought over to the UK and US the translator screwed up horribly on the conversions at first. Partly by not really even doing them. Just substituting the metric unit with the rough alternative, but keeping the numbers.
** Many people like to sound clever by pointing out that ''Literature/TwentyThousandLeaguesUnderTheSea'' is 60,000 miles, and thus impossibly deep (the deepest part of the ocean is less than 3 leagues down), but this figure is the distance travelled in the book, not the depth they reach. But "Twenty Thousand Leagues Whilst Under The Sea" isn't quite as pithy.
*** Verne consistently used a metric league (lieue, if you wish) of exactly 4 km in his works, thus the name translates into 80,000 km or ~50,000 statute miles, or almost exactly double circumnavigation (there's only a single one in the book, due to inevitable deviations from the shortest route). However this again brings the confusion as in Belgium the metric lieue is defined differently than in France and corresponds to five kilometers instead of four.
* ''Literature/TheCulture''. In LookToWindward, Hub frequently refers to interstellar distances in large numbers of "year". Not light-years, YEARS.
* In the original version of Creator/MarionZimmerBradley's ''[[Literature/{{Darkover}} The Bloody Sun]], the protagonist is told that his matrix jewel can probably emit "only a few grams of energy."
* Used in Robert Asprin's ''Series/MythAdventures'' series; as a dimension-traveler stranded in a backwards world, Aahz has trouble with Klahdish units of time and often has to be corrected by his apprentice Skeeve.
* In ''Literature/EncyclopediaBrown'''s defense, one story referenced this trope in its solution: a man claiming to be a sailor is [[ConvictionByContradiction revealed as a fraud]] because (among other mistakes) he refers to speed in terms of "knots per hour", when a knot is ''already'' a measure of time over distance, i.e. one nautical mile per hour.
* ''Literature/PerryRhodan'' plays with, then in-setting justifies the "temperatures below absolute zero" version: in the first arc in which humanity and allies seriously and consciously have to fight off the self-styled forces of cosmic chaos, one of the latter's weapons is a phenomenon that does indeed cause objects caught in it to rapidly cool down to absolute zero and below...whereupon they simply ''vanish'' from a universe in which they can no longer exist. In reality, they end up getting displaced into another universe whose own 'absolute zero' is in fact several hundred kelvins below that of ours, a fact that is discovered once actual survivors of the whole process start to [[CameBackWrong come back]]...
* In a travel guide by comedian Dave Barry he facetiously lists a kilometer as a unit of foreign currency.
* In ''Literature/TheScrewtapeLetters'' Screwtape uses "light-year" as a measurement of time.
* ''{{Fahrenheit 451}}'', supposedly titled after the flash point of paper. Which is, actually, about 451 degrees ''Celsius''.
** It depends on the paper material. Paper made from wood pulp ignites at about 220 to 240°C (420 to 470°F). The [[http://books.google.co.in/books?id=qa-I8QAOUL8C&pg=PA406&redir_esc=y paper that talks about an ignition point of 450°C]] is referring to paper made from rayon fiber, or even cotton.
* In ''The Truth about Pyecraft'' by Creator/HGWells, A fat man called Pyecraft persuades the Narrator (who has some magical recipes from his great-grandmother) to give him a potion to let him lose weight. Unfortuantely, while Pyecraft ''does'' lose Weight, he doesn't lose ''Mass'', and ends up floating near the ceiling.
* ''EarthTheBook'' ends with a survey for the reader to full out as an "Application for Genetic Reconstitution by Aliens." One of the questions is "How many kilowatts would you say your brain produces hourly?"
* In one short story, a boy thinks he's dying of a fever, having heard that you can't live with one much more than 40 degrees, and he has one that's over 100. His father points out the difference between Celsius (the former) and Fahrenheit (the latter), comparing it to miles and kilometers. [[JustifiedTrope Justified]], considering that the boy is young enough to not know.
* An in-Universe example in ''Literature/HitchhikersGuideToTheGalaxy1'' concerns the unfortunate fate of the combined battlefleets of the Vl'hurgs and G'Gugvunts, sent out to annihilate humanity after it is discovered exactly who it was who started the terrible war between them. Unfortunately, due to a terrible miscalculation of scale, the thousands of horribly beweaponed warships were swallowed by a small dog.
* Exaggerated in ''Literature/DaveBarrySleptHere'', which gives the distance of West Berlin behind the Iron Curtain as "120 miles (325 kilograms) (30936.54 hectares) (2,342,424,323.3432 millipedes)." That's one unit of distance, one unit of mass, one unit of area, and one class of arthropod.
* In the short story ''Retrograde Summer'', JohnVarley [[SubvertedTrope managed]] to use “light year” as a time span. On Mercury, a (solar) day is as long as two years, so you have a light year (that half day=year when the sun is up), followed by a dark year (sun below the horizon), followed by a light year...
* ''Literature/BoredOfTheRings'' has a footnote defining a league as "approximately 3 furlongs or only a knot short of a hectare."
[[/folder]]

[[folder:Live Action TV]]
* ''{{Bones}}'' once referred to "Force in Newton-Meters." Unfortunately, the newton-meter is a unit of ''torque'', equivalent to one joule per radian.
** The Newton-meter is also a unit of energy equivalent to the joule (as radians are dimensionless); in this case, the meter is the linear distance over which the force is applied rather than the distance from the fulcrum. Nevertheless, it's still not a unit of force, which is simply Newtons.
* Even ''Series/MythBusters'' made the "watts" mistake, displaying a chart showing the power consumption of light bulbs in "watts per hour".
* On an episode of ''Are You Smarter than a Fifth Grader'', one of the quiz questions was "How many watts are used during one kilowatt hour?" (The answer given was 1,000, but the question as written is unanswerable since one kilowatt-hour can result from using 2000 watts over a half-hour period, 500 watts over a two-hour period, or any of an infinity of other possible combinations.)
** Not to mention the fact that the phrase "during one kilowatt hour" is just plain wrong as it implies a kilowatt hour is a unit of time (it is a unit of energy, equal to 3.6 Megajoules).
* In an episode of ''Series/StarTrekVoyager'', the power output of the warp core is given in "teradynes per second". Dynes are a unit of force, not energy.
** Although this could just mean that the warp core's power could be used to ''exert'' X teradynes of force.
** Several Star Trek episodes have used the word "teradyne" as a unit of computer processing power. "Dyne" in the Trek universe seems to mean "a small amount of whatever it is we're talking about right now."
** The ''Voyager'' writers had trouble even keeping ''their own fictional units straight''. On at least one occasion, "cochranes" were used (quite incorrectly) as a measure of explosive yield, rather than the proper usage as a measure of warp field strength.
*** To be fair, real life nuclear explosive yield figures tend to be in kilotons and megatons (equivalent of TNT), instead of joules. Maybe people in Voyager still have no grasp of how much a joule is, so use some kind of Cochrane equivalence instead.
*** The term "iso", has been added to both tons and rems (a measure of radiation). Iso means "equal" or "homogenous", suggesting that it's either meaningless (e.g. 6000 isorems means 6000 rems), some weird "equivalent to that much as far as we're concerned" shorthand taking into account bizarre ''Star Trek'' science or as ''SFDebris'' suggested, as the term is often used when someone's explaining how screwed they are, means "It's 6000 fucking rems out there!"
*** In one novel, they used something called a "Cochrane radius", which is basically the minimum distance from a star at which it is safe to engage a warp drive. If a warp field is created within that radius, the star would go nova. Of course, since this has happened on several occasions in the show without any ill effects, it can be safely said that this is bullshit.
** The episode of ''Series/StarTrekTheNextGeneration'' "The Royale" listed a planet's surface as being -291°C. Not only is it below absolute zero (-273.15°C), but it's really, ''really'' unlikely to occur naturally on a planet, thanks to the physics explained in SpaceIsCold. This was due to someone deciding to swap out the word [[TheMetricSystemIsHereToStay "Fahrenheit" with "Celsius" at the last minute]].
* The light-year confusion is brought up in an episode of ''The Big Bang Theory''. Penny is talking to Sheldon (a theoretical physicist) and says something like "I guess you would say '''light-years'' ahead of his ''time'''". Sheldon responds, "I wouldn't say that. Nobody would. Nobody who knows what they're talking about, anyway."
* Chloe Sullivan also does this a couple of times in Smallville. For instance (in the context of a discussion involving time travel):
-->'''Clark:''' You're saying Kara's actually on Krypton.\\
'''Chloe:''' Well, Krypton 1989. Give or take a few light-years.
** That makes it sound like she may or may not have been left drifting in deep space. Unfortunate implications, indeed!
* In the ''Series/BabylonFive'' episode "Messages from Earth", one spaceship evades another by hiding in the atmosphere of Jupiter. The pressure on the exterior of the ship as it descends is given in "gravities", although gravities are a measure of acceleration and not pressure, which is very different.
** An example involving a unit made up for the show. Early on, it was decided that time on the station would be measured in cycles, possibly to avert TwoOfYourEarthMinutes. Unfortunately, none of the writers seemed to be able to agree on what a cycle was equivalent to (i.e. is it an hour? A day? A minute?). The idea was scrapped before the end of the first season. This was {{Lampshaded}} in a later episode when Ivanova stated that she was going to hold some troublemakers in custody for a Drazi cycle, after which the problems they were causing on the station would be sorted out. The Drazi she's explaining this to laughs, and points out that a cycle is a Drazi ''year'', not a Drazi month.
* In the documentary ''Series/ForensicFiles'' on TruTv, it is stated that a gunshot produced 120 decibels of sound, and that 70 decibels, or "about 60%" of that, went through to an adjacent room. The decibel scale is logarithmic, with 20 dB being equivalent to a factor of 10 increase in (Pa) amplitude, so 70 dB is really about 0.3% of 120 dB measuring by the raw pressure function.
** For comparison, 120 dB is just short of the pain threshold, about as loud as sitting in the front row at a rock concert or using a power saw. 70 dB is a little louder than a normal speaking voice. For the sound of a gunshot heard through a wall, the 60% figure seems accurate; the 70 dB not so much.
* Some sci-fi shows attempt to rectify such things by actually using the alien standards of time (see {{Microts}}). "Cycles" are a big favorite. ''Series/{{Farscape}}'' is probably the most easily notable of these, with its microts, arns, and cycles. While a microt seems comparable to a second, an arn to an hour, and a cycle to a year, the actual usage definition seemed to be "An arn is longer than a microt and a cycle is a really long time." Since the scales for them were never actually defined, they were just as long as they needed to be for the show's purposes.
** In "Through the Looking Glass", Crichton asks D'argo to wait five minutes or four hundred microts. Using this, one microt would be 0.75 seconds.
* In the last season of ''Andromeda'', Rommie refers to having been shut down for ''nanomillennia'' as if that's a long time. Nano- is a prefix meaning one billionth. One ''nanomillennium'' is about 31.5 seconds. One thousand ''nanomillennia'' is still less than one day. This might be considered a long time to a computer, but since Rommie had been offline for longer periods previously, that makes it a mistake.
* The plot of one episode of ''TheMiddleman'' revolves around "4000 angstroms of [[DoctorStrangelove Balthorium-G]]"; an angstrom is a unit of length, not mass or volume. WordOfGod is that the writers were perfectly aware of this, but did it anyway because they thought [[RuleOfCool it sounded better]].
** Better yet the angstrom is equal to a tenth of a nanometre and is used because its about ''the diameter of an atom''. So 4000 angstroms is only 0.4 micrometers, or less than a bacterium (which are between 1 and 10 microns) long.
* The episode "Getting Barry Higher In The World" of ''LastOfTheSummerWine'' features Seymour enlisting Wesley to build them a kite, but Wesley assumes that because Seymour's a pompous schoolteacher with a university education, all the figures on his plan are in metres rather than feet. The kite comes out over three times too large, but when it turns out to work as a hang-glider, Seymour claims IMeantToDoThat.
* In ''BostonLegal'', opposing counsel threatened to "drag it out for light-years" if the main characters declined a settlement offer. ([[HandWave How far the pages will stretch?]])
* In an episode of the obscure Australian series ''Ship to Shore'', a report (later revealed to be false) came in of a tsunami 30 feet (10 meters) high came in. Since some of the older islanders still used [[AmericanCustomaryMeasurements imperial units]], the confusion snowballed to the point that the wave was supposedly 900 meters (3000 feet) high, and the islanders prepared for Armageddon.
* ''TopGear'' has a tendency to parody this. James May, being GoodWithNumbers, gives accurate conversions but refers to metric and imperial respectively as 'Roman Catholic' and 'Church of England'. Jeremy Clarkson on the other hand deadpans complete nonsense such as measuring torque by spreading his hands apart and saying 'about that much'.
* An episode of ''SaturdayNightLive'' hosted by Kelsy Grammer highlighted the confusion pointed out above regarding ''Literature/TwentyThousandLeaguesUnderTheSea''. Nemo calmly explains that he misspoke and he should have used fathoms to indicate depth. However, the other characters (even TheProfessor) end up describing every unit of measurement, even '''time''', in terms of leagues, leading to Nemo being brought to the edge of madness before being dragged away by a giant squid.
-->'''Narrator''': The entire crew of the Nautilus - all 20,000 leagues of them - searched for Captain Nemo for over 20,000 leagues and nights. 20,000 leagues later, they still hadn't found a trace of Captain Nemo, the man they called.. Ol' 20,000 Leagues Under The Sea!
-->'''Captain Nemo''': [[BigNo Noooooooo!!!!]]
* ''Series/KamenRiderFourze'' acknowledges the light-year issue in episode 12, when space {{Otaku}} Yuuki meets the school's chairman, a former astronaut. She says she's read his book "for light-years" and he immediately responds "Incorrect, light-years are a measure of distance". Rather than a mistake, however, it seems that Yuuki said this on purpose as a pretext to quote more of his book.
* The ''Series/{{CSI}}'' episode "Overload" includes, among its many atrocities against physics, Grissom confidently stating that "terminal velocity is 9.8 meters per second squared". High school physics should be enough to know that meters per second squared measure acceleration, not velocity (terminal or other).
** In the season 14 episode "Girls Gone Wild", the team tries to find a grow op in a small town by checking the power consumption of houses in the area. Unfortunately, they mix up watt hours and watts, leading to them describing an average home as using 900 kW and their suspect using a whopping 5 MW. That little town would have needed its own nuclear reactor...
* At one point in ''Series/StargateSG1'', the team is in a rapidly-cooling room and needs to find a source of heat. Carter informs everyone that they just "passed -40 degrees". Jackson asks if that's [[SubvertedTrope Fahrenheit or Celsius]], and Mitchell responds that it doesn't matter: the [[ShownTheirWork two scales are the same at that point]].
* Defied in many episodes of ''Series/GoodEats'', where Alton Brown instructs his viewers to measure out X ounces of a dry good ''by weight''. The emphasis on weight has two purposes: first, weight is generally a more precise indication than volume; second (and more relevant to this trope), it's so that viewers ''don't'' try measuring by volume (i.e. in ''fluid'' ounces).
[[/folder]]

[[folder:Music]]
* The Music/ChrisDeBurgh song "A Spaceman Came Traveling" (a sci-fi interpretation of the first Christmas) explicitly refers to "light-years of time"; the writer not only makes the mistake but goes out of his way to wave it in the listener's face.
* Music/JoanBaez also made the light-years mistake in "Diamonds & Rust".
* The Music/{{Sparklehorse}} album ''Dreamt for Light Years in the Belly of a Mountain''. Perhaps the mountain was hurtling through space.
[[/folder]]

[[folder:Radio]]
* One of the many possible definitions of the diagonal in [[Radio/ImSorryIHaventAClue Mornington Crescent]] (specifically Archbald's Metropolitan Logorhythmic Progression) states "the diagonal shall be agreed to be any angle being agreed to be an angle between the angle of one degree and the angle of three hundred and fifty nine degrees ... Celsius".
[[/folder]]

[[folder:Tabletop Games]]
* As a "watts" example in reverse, {{GURPS}} sourcebooks insists on referring to kilojoules as "kilowatt-seconds". Although technically correct this is inelegant and confusing and proof that, even with the constant calls for them to abandon Imperial units, Steve Jackson Games shouldn't be let loose with SI.
** They can't even keep that much straight. Centimeters get used from time to time, generally for weapons. More confusingly the abbreviation mps is used to talk about mile per second despite the fact that even people in the US think of it as meters per second.
*** That bit Steve Jackson at least gets correct. The abbreviation for meters per second is m/s and nothing else.
** In at least one ''GURPS Traveller'' supplement, there's an extended sidebar on the difference between short tons, long tons, metric tons, water-displacement tons, and ''liquid hydrogen''-displacement tons, all of which have some relevance in the setting. (A "100-ton ship", in ''Traveller,'' has a volume equal to 100 ''metric'' tons of LH2.)
[[/folder]]

[[folder:Video Games]]
* ''VideoGame/PokemonRedAndBlue'' (as well as their remakes, ''[=FireRed=]'' and ''[=LeafGreen=]'') referenced the light-year mistake with the Junior Trainer (Camper in the remakes) in Brock's gym, saying you're [[YearsTooEarly "light-years from facing Brock"]], but then acknowledging the mistake after you beat him.
* An infamous example occurs in the lawnmowing minigame in ''VideoGame/NoMoreHeroes'', where "square meter" has been [[CulturalTranslation culturally]] [[BlindIdiotTranslation "translated"]] into "acre" (roughly ''four thousand'' square meters).
* In the various incarnations of ''VideoGame/SimCity'', each tile square is also supposed to be 1 acre. Yet a tile square is only big enough for a single one-family house with hardly any yard, and it takes 4 adjacent tile squares to build even a small apartment building. This could be hand-waved as just being a representation of an acre of homes, until you realize THE ROADS ARE AN ACRE WIDE (actually over 60 meters wide).
** Corrected in ''Sim City 4'', where the [=FAQs=] explicitly state that the length a tile is 16 meters. This means that small "cities" are roughly 1 square kilometer and the largest ones are 16 km^2. (Best to think of the individual "cities" as neighborhoods and the overall "region" as a metro area.) However, this introduces FridgeLogic in its own right when the player realizes that school buses won't travel more than about half of a kilometer from their respective school to pick up kids, which is usually the ''minimum'' distance that school bus service ''begins''.
* ''VideoGame/MetroidPrime 2'' manages to do this with its [[{{Microts}} fictional measurement of time]], the cycle. While the length of one cycle is never really stated, based on its use in the Space Pirate logbooks it would seem to be analogous to something between a few months and a year. However the Luminoth elder U'mos is described as being several centicycles old. They probably meant several hundred cycles, but the prefic centi means one-hundreth. Presumably the writers either weren't aware of the correct prefix, or just decided it sounded cooler than "hectocycle".
* ''VideoGame/GhostTrick'': In the ending, Beauty and Dandy are breaking into a safe above Chicken Kitchen with gunpowder. Dandy reads the instructions for twenty ''kilo''grams of gunpowder instead of twenty grams.
* The manual for ''{{VideoGame/Fallout}} 1'', written from an {{in universe}} perspective from Vault-Tech (the company which made the vaults), suffers from several mistakes in one unit when it gives the technical specifications for Vault 13. Among them is: "Power requirements.....3.98mkw/day". Even assuming that the w is supposed to mean Watts (which have the symbol W, being named after a person), Watts per day is a nonsense as explained in numerous other examples, as Watts are a unit of rate of use of energy on their own. Even 'mkW' is also, while arguably a valid unit, ridiculous, as it would be 'millikilowatts', which would simplify to just 3.98 Watts (while an average kettle will use something in the range of 2-5 kilowatts!). '[=MkW=]' would be the slightly more reasonable 'megakilowatts', but this would still lead to the question of why they didn't simplify it to gigawatts, the same unit. {{Justified}} somewhat in that Vault-Tech is portrayed throughout the manual as tending to cut corners and not being very knowledgeable about what they're doing.
[[/folder]]

[[folder:StandUpComedy]]
* Comedian [[http://drpetecomedy.com Dr. Pete Ludovice]] has a routine where he suggests that men try to invoke UnitConfusion by reporting their [[GagPenis penis size in nanometers]].
** There is a joke where a woman is telling her friend about a guy's penis and claims it's 700 nanometers. The other woman is astonished that it's so small, but the first woman replies that the penis is that red (the wavelength of the color red is 620–750 nm). Somewhat of a subversion- both use the same system of measurement, and it's used correctly, but the ''context'' was what was missing.
* In one of his routines, Tim Steeves opined that Americans think Canada is so cold because weather maps measure Canadian temperatures in Celsius and American in Fahrenheit, extrapolating that to a scenario where colonial explorers demarcated the border between the US and Canada because the temperature abruptly dropped forty degrees. [[note]]As it happens, Canadian weather reports actually give ''both'' measurements for the benefit of visitors from the United States and/or older folks who never got the hang of metric.[[/note]]
[[/folder]]

[[folder:Webcomics]]
* Early ''Webcomic/SchlockMercenary'' strips have a nasty habit of referring to "watts of energy." Even as late as the third book, while it gets right that terawatt-nanoseconds would be a unit of energy (one more commonly known as the "kilojoule"), it treats it as though nanoseconds make it more incomprehensibly huge than "terawatt-hours" or, say, "terawatt-millennia."
** It also plays with this trope with some things, such as freem, which are explained as the amount of pay a "Poliflorian Hypernetter earns about two thousand Freem during one Efrickalian work-week."
** Comparison of [[http://www.schlockmercenary.com/d/20050208.html two]] [[http://www.schlockmercenary.com/d/20050305.html strips]] from the ''sixth'' book suggest he's confused diameter and radius.
* ''Luke Surl'' [[http://www.lukesurl.com/archives/1607 shows]] a confusion of angle units [[ExpositionDiagram on a chart]].
* ''SaturdayMorningBreakfastCereal'' shows [[http://www.smbc-comics.com/index.php?db=comics&id=330 self-explaining one]].
* In ''Webcomic/SequentialArt'' squirrels try to build [[http://collectedcurios.com/sequentialart.php?s=581 giant robots]] to fight a giant bug and forgot to agree if they are using [[http://collectedcurios.com/sequentialart.php?s=582 millimeters or centimeters]]. But they like the resulting battle armor [[http://collectedcurios.com/sequentialart.php?s=583 even better]].
* In {{WebComic/Homestuck}}, Terezi claims to be 6 in her first conversation with Dave, who is kind of shocked. Though, [[AnachronicOrder at this point of the story]], the reader is aware that [[ExpospeakGag Alternian Solar Sweeps]] are longer than Earth years. To clarify, trolls are about the same age as the kids (13 years).
[[/folder]]

[[folder:Web Original]]
* Happens in universe in an Wiki/SCPFoundation story. There is a big difference between mA and MA. Exactly how he managed to set the circuit to nine orders of magnitude lower than normal isn't given.
[[/folder]]

[[folder:Western Animation]]
* The protagonist of the children cartoon ''Jimbo'' is a talking Jumbo-jet that was manufactured in centimetres instead of inches by mistake.
* In the episode of ''HeyArnold'' where they try to get into the world record book, their attempt at the largest pizza pocket fails when Sid misinterprets "tsp" for the [[ImpossibleLeavening yeast requirement]] as "ten square pounds" instead of "teaspoons".
* In one episode of ''WesternAnimation/EdEddNEddy'', Edd is working on an old radio, and realizes he'd mistaken a "fifteen-amp resistor" for another part. The problem is, amps are used to measure ''current'', and the ''ohm'' is used to measure resistance. Resistors have power handling specifications too, but the unit for those is the watt, so that doesn't help.
* In ''WesternAnimation/TheSimpsons'', Crazy Vaclav asserts that the car he's trying to sell will "do 300 hectares on a single tank of kerosene". The hectare is a measure of area, not distance. Can be justified by the fact that Eastern European cars would be used for agricultural purposes and buyers would want to know how much of their fields they could cover per unit of fuel.
** Grampa Simpson hates the metric system. "My car gets forty rods to the hogshead, and that's the way I likes it!" [[note]]If you're curious, that's approximately 120,000 liters per 100 km (0.002 miles per gallon). It must be a Hummer.[[/note]]
** Mr. Burns has trouble with metric too, like in the episode he drops a weight marked "1000 grams" (just over 2 lbs) on Homer, to his minor annoyance, and then comments that it sounded much heavier when he ordered it.
** In the episode where Bart goes to a gifted school, the kids con him out of his lunch by using units like picolitres to make it sound like they were offering more than they were.
** In the beginning in one episode where Homer takes the kids to school, he uses a GPS which gives him the distances in meters. The confusion leads him through a construction zone.
* In the ''FamilyGuy Star Wars'' movie ''Blue Harvest'', Han Solo (Peter Griffin) claimed that the Millennium Falcon completed the Kessel Run in less than 12 parsecs. Luke (Chris Griffin) then tells an astonished Han than parsecs are a measure of distance not time.
* In ''{{Transformers}}'', (well, some series, anyway) "light-year" has been a unit of time.
** ''Transformers'' has more [[http://tfwiki.net/wiki/Units_of_time units of time]] and [[http://tfwiki.net/wiki/Units_of_length distance]] than you can shake an exhaust pipe at. Most of them have never been explicitly defined, so any of them could be this trope.
* An in-universe example: in ''Jimbo and the Jet Set'', Jimbo's diminutive size is explained in the [[IncrediblyLamePun pilot]] episode as being the result of his designers mistakenly using centimetres instead of inches.
* The French version of ''WesternAnimation/{{Thumbelina}}'' (''Poucelina'') has the Prince singing [[http://www.youtube.com/watch?v=EKe5jzvUk8w "Depuis des années-lumière, je n'attends que toi."]] ("For light-years, I've been waiting for you.").
* In {{JohnnyTest}}, the girls have used Newtons as a unit for magnetic force. While technically correct, Teslas would have been a much better unit, because they measure the strength of the field. The force also varies with the velocity of the charged particle.
* In an episode of ''SpidermanTheAnimatedSeries'' Spider-man specifies a frequency in microfarads. Frequency is normally measured in hertz whereas the farad is a unit of electrical capacitance. The fact that Spider-man was smart enough to be able to guess the correct frequency for the TechnoBabble that he was trying to pull off should have made this mistake unthinkable.
[[/folder]]

[[folder:Real Life]]
* In real life, the results of metric confusion can be very catastrophic and expensive, as when the Mars Surveyor '98 Orbiter crashed and was destroyed in 1999 -- the "small impulse" analysis software was giving data in pound-seconds, while the mission navigation team was expecting data in Newton-seconds.
** During World War 2, a mission to supply Malta by airplanes taking off from an aircraft carrier ran into grief because the Royal Air Force (which supplied the airplanes) thought that the distance they would have to fly was in statute miles. But the distance had been given to them by the Royal Navy, which of course used ''nautical'' miles. (1 nautical mile = 1.151 statute miles).
** This was also [[ExploitedTrope used fraudulently]] by 19th-century colonists in South-West Africa (modern Namibia) who purchased land up to a distance of so and so many miles inland from the coast from local tribes. What they did not mention in the negotiations, but wrote down in the contracts was that the distance specified was not in the British statute miles (1 mile = 1.6 km) familiar to the tribal leaders through contacts with e. g. South Africa, but used the less familiar geographical or German mile (ca. 7.5 km).
* A more down-to-Earth example (no pun intended) was the [[http://en.wikipedia.org/wiki/Gimli_Glider Gimli Glider.]] The Boeing 767 C-GAUN was the first Air Canada jet with metric instrumentation. There already had to be a measurement conversion because the refueling people on the ground measured kerosene in volume (gallons), while the aircraft measured fuel in weight (pounds or kilograms). The ground crew used the wrong conversion factor in calculating how many gallons to pump on the plane, leading the crew to think the plane had 22,000 kilograms of fuel on board, the amount needed for the flight, when it only had 22,000 pounds (9979 kg). The exact mass of fuel used is very important to aircraft and thus the gauge could not be replaced with a car style unitless gauge.
** And in a supreme GuideDangIt (for the pilots/groundcrew)/WhatAnIdiot (for Air Canada) moment: ''nobody on the groundcrew or in the cockpit had been trained to do the proper conversion''.
*** This was primarily due to the fact that this kind of thing used to be the job of the flight engineer. Unfortunately, computerized jets like the Boeing 767 have eliminated the need for that position, and apparently no one at Air Canada had stopped to consider who should take over the FE's duties.
** Fortunately, due to [[AcePilot supreme skill of the pilots]] and some good luck they managed to land the powerless plane (that's why it's commonly called ''Glider'') on the former RCAF Gimli airbase, where one of the pilots was stationed back in his military days, and managed not to hit the drag races held on the runway they landed on, so [[EverybodyLives nobody got hurt]] both on plane and on the ground. Note that in later simulator re-creations of the circumstances with other flight crews, ''every one'' ended with a fatal crash.
** Under normal circumstances, the fuel sensors would detect the actual amount of fuel loaded and that would prevent the problem. However, the fuel sensors were broken on that particular plane, which they actually knew, but this was not considered a serious enough fault to ground the plane. Without the sensors, the pilots depended on the FMC's calculated fuel weights to track fuel consumption during the flight, but because it had been given an incorrect starting weight, all its calculations were based on that and therefore also wrong.
* A fatal example of this trope occurred with [[http://en.wikipedia.org/wiki/Korean_Air_Cargo_Flight_6316 Korean Air Cargo Flight 6316]]. As the plane was climbing, ATC cleared the flight to 1,500 meters (4,900 feet). The flight crew misinterpreted this order as 1,500 ''feet'', leading them to believe they were too high. The captain attempted to descend, but pushed the control column too hard, causing the plane to nosedive into a neighborhood, killing all three crew members and five people on the ground.
* Apparently a legal aversion: some people like to snark that 'pound' is weight (meaning the force of the object being pulled down), while 'kilogram' is mass, and the two aren't really the same. A notebook from the National Institute of Science and Technology specifically stated that as far as packaging, the two were pretty much the same. For most use on Earth, they are, anyway.
** Of course they are not the same! One kilogram is more than twice a pound!
** That's because the mass-to-weight ratio is a constant on Earth (or close enough: on average g = 9.81 m/s^2 or 32.2 ft/s^2) meaning there is a linear correlation between mass and weight. On Earth it pretty much means the same thing then. However, move to environments with a different gravity (basically any other planet or moon, although the correlation will be linear on that world) or even space (where weight becomes meaningless) and you get a different story. Even worse: if you launch the object from a planet and into space, the gravity exerted on the ship becomes variable (inverse square law) meaning the correlation between mass and weight is no longer linear.
** In scientific literature, you may find references to the "pound-mass" to refer to that concept, abbreviated "lbm", mainly because the Imperial unit of mass, the slug, is stupid. Whether that particular convention is followed or not, though, is hit or miss.
*** Made even more confusing since sometimes "lbf" is used for "pound-force", so sometimes you'll have "lb" (pound-force) and "lbm" (pound-mass), or "lb" (pound-mass) and "lbf" (pound-force) used in text. Best to just always stick with "lbf" and "lbm" and eliminate confusion.
*** Of course serious modern scientific literature should use the SI or units which are typically used in the field.
*** A standard measure of rocket engine performance is called the "Specific Impulse", which defined as the thrust per fuel consumption -- or in traditional units: seconds of pounds (force) per pounds (mass). Dividing out the pounds, Specific Impulse is therefore reported in "seconds". In SI units, it's second-Newtons/kilogram, which simplifies to m/s. In the basic rocket equations, specific impulse corresponds to the exit velocity of the exhaust.
* Precious metals are measured in troy pounds (373 g), which are divided into 12 troy ounces (31 g) -- standard ("avoirdupois") pounds (454 g) are divided into 16 ounces (28 g). (Hence, an ounce of gold weighs more than an ounce of feathers, but a pound of gold weighs less than an pound of feathers.)
** [[http://www.youtube.com/watch?v=XI9w8g4UT2I This video]] shows more examples of units with the same names but different values (e.g. short tons vs. long tons, statute miles vs. nautical miles vs. imperial nautical miles, etc.).
* There's a story about a guy from Indonesia who got fired from a multinational company because he measured an ounce as 100 grams and a pound as 500 grams, which resulted in years of equipment malfunctions. It turned out that [[http://en.wikipedia.org/wiki/Dutch_units_of_measurement such units were once used in the Netherlands]] (called ''ons'' and ''pond''), and although they're not formally used anymore today, the guy's home country, that is a former Dutch colony, keeps teaching it at schools.
** This is because at the time the metric system was introduced into the Netherlands (in the 19th century), the ons and pond were the Dutch equivalents of the English ounce and pound, with approximately the same weights. They were redefined in metric terms to ease the transition, but unlike some other such measures never really fell out of use, though they really only get used for day-to-day measuring. Even today, many people ask for things like "an ounce of minced meat" when they want 100 grams. Very, very few of them will know that such an ounce was ''not'' always 100 grams — including translators, who often translate the English word "ounce" with either "ons" or "100 grams", making the quantity over three times as big at a stroke. Oh yeah, and don't even try finding a translator who knows how big a fluid ounce is.
*** Cases similar to the Dutch case can be seen in Greater China as well. Traditionally , 1 [[http://en.wikipedia.org/wiki/Catty catty]]= 16 [[http://en.wikipedia.org/wiki/Tael taels]]=160 [[http://en.wikipedia.org/wiki/Mace_%28unit%29 mace]]= ~600g. In 1959, however, Communists introduced a similar transition scheme, where 1 catty=10 taels=100 maces=500g. Of course, the jurisdictions that are not under direct Beijing control--UsefulNotes/{{Hong Kong}}, UsefulNotes/{{Macau}} and UsefulNotes/{{Taiwan}} didn't follow. This is particularly confusing as these Chinese units of measurements are still in common use for foodstuff and precious metals..
* At least in Germany, instead of saying "kilometre per hour", many people tend to use the abbreviation "km/h" or in everyday conversation. But only the letters are said out loud, not the slash. If this unit wasn't so ubiquitous, you could easily mistake this for "kilometre ''multiplied by'' hour".
** Some also still use the vernacular expression "Stundenkilometer", which also would be translated as "hours multiplied by kilometres".
* At least in Canada, people will sometimes use (or at least recognize) the military slang "klicks" as an abbreviation for "kilometre" and also use it as an abbreviation for "km/h", meaning there's a difference between "I have to go 20 klicks" and "I have to go ''at'' 20 klicks."
* Ubiquitous before the introduction of metric measures, because every country had its own value. NapoleonBonaparte was five foot two in French units, but five foot six in British units.
* Carats and karats should not be confused; one is a unit of mass and the other is a unit of purity, respectively. Gems are measured in carats, with 1 carat = 0.2 grams. Gold is measured in karats, on a scale of up to 24.
* In 2004, Switzerland and Germany wanted to build a [[http://de.wikipedia.org/wiki/Hochrheinbr%C3%BCcke bridge over the Rhine]], starting from both sides. To meet in the middle, they agreed to build it on a certain height above mean sea level. Unfortunately, the Germans measured in height above the North Sea, while the Swiss measured in height above the Mediterranean Sea, which differ by about 27 centimeters. The constructors were aware of that difference, but subtracted it from the wrong side, leading to a final height difference of more than half a meter.
* Even unitless numbers can suffer from similar problems. In the US (and since a lot of other countries around the world have adopted the convention) a million is 10^6, a billion is 10^9, a trillion is 10^12, and so on. So the prefix n (Latin for one, two, three etc) the "short scale" is used determines the number by 10^(3n+3). However in other countries that still use the old British/European "long scale" ([[NonindicativeName no longer used in Britain]] since 1974), a million is 10^6, a billion is 10^12, a trillion is 10^18, and so on (using the formula 10^6n). This is why scientist forgo using words and write large numbers in scientific notation instead.
** Also, since all countries at least agree that a million is 10^6, sometimes larger numbers will go unused in favour of stating in millions. 10 thousand million million million is unambiguous, for instance, whereas while in the US and elsewhere it would be typically referred to as 10 sextillion, but some people in [[WithEuropeButNotOfIt Britain and Europe]] would call that 10 thousand trillion (or in French possibly, 10 trilliard).
** The Chinese used to have the same problem with their own words for big numbers. Although nowadays most people never use any number above 亿 (10^8), there are at least [[https://en.wikipedia.org/wiki/Chinese_numerals#Large_numbers four different ways]] to interpret the higher numbers like 兆, 京, and 垓. Today, everybody agrees that 亿 is 10^8, which means method 1 is no longer used. The structure of methods 2 and 3 are reminiscent of the short and long scale in European numbers (modern Chinese people always use method 2 if they use the larger numbers at all), while method 4 is the basis for Donald Knuth's [[https://en.wikipedia.org/wiki/-yllion -yllions]] system.
* One example of unit conversion confusion comes from a puzzle on [[https://research.microsoft.com/en-us/um/people/leino/puzzles.html this page]], which talks about a peculiar instruction on a page of a recipe cookbook that was originally written using the Celsius scale and was translated to use Fahrenheit: "If your oven has a fan, reduce the recipe temperature by 68°F." Because the zero points of the Celsius and Fahrenheit scales are different, converting between ''differences'' in temperature is different than converting between the temperatures themselves, and the difference of 20°C (36°F) in the original recipe book becomes a little over 37­°C when "converted" in this way.
* For many years, computer memory units used prefixes that looked like SI prefixes, but were subtly different. The Kilobyte was 1024 bytes, for example. This all went horribly wrong one day when an enterprising Marketer realised they could sell harddrives with storage capacities measured in megabytes... but using the SI meaning of mega (10^6), not the computer engineering meaning of mega (2^20). Result? Sell smaller drives, but claim the same size, thus undercutting competitors who spent more to make bigger drives because so many consumers didn't stop to check the difference.
** There are now new standard prefixes like 'kibi' and 'mebi' (short for kilo-binary and mega-binary, respectively) to mean 1024 and 1048576 respectively, but they've so far failed to be embraced by the hardware and software community outside of harddrive manufacturers.
* Data bandwidth, whether from a network or local peripheral bus (like USB) express speed in raw data rates, not usable data rates. And it will always use bits per second (using a lowercase b) and not bytes per second (using a capital B).
** For example, the hard drive bus SATA has a raw data rate of 6 gigabits per second. But it uses 8/10b encoding (where 8 bits are padded to 10), making 20% of the bandwidth unusable. The there's SATA protocol overhead. After all that, the maximum data rate is about 4.4 gigabits per second per second, seeing this is the ceiling for most SSDs.
[[/folder]]

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