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Common mistakes when using the metric system

44 点作者 stereoabuse8 个月前

17 条评论

ikari_pl8 个月前
I was surprised to see &quot;L&quot; as the &quot;only correct&quot; (though as minor mistake) abbreviation for a liter, being certain &quot;l&quot; or &quot;ℓ&quot; is the way to go, as that&#x27;s how I was taught so far. Turns out that SI actually allows both &quot;l&quot; and &quot;L&quot;, but I would only ever use the uppercase if it&#x27;s a sans-serif font in a non-prefixed unit (&quot;L&quot; as opposed to &quot;ml&quot;). I&#x27;ve never seen any can or bottle using &quot;mL&quot; or &quot;cL&quot;.<p>Some of the examples go pretty far too, either calling spelling I&#x27;d never see a &quot;common mistake&quot; (like &quot;gr.&quot; for grams), or by being too scientifically correct for a casual usage, for example in a press article (&quot;(100 + 200) grams&quot;, right).<p>But then I saw &quot;Set the oven to 450 K&quot;, and I realized that the examples are to be taken with a grain of salt :)
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physicsguy8 个月前
Lots of these are country dependent in terms of what is familiar to people. To some degree that matters if your primary communication is not international but domestic.<p>For e.g. in the UK sqm is very common, particularly when looking at property. On RightMove which is the most popular property website here, for e.g. you can see here that the default is `sq ft` with `sq m` given underneath: <a href="https:&#x2F;&#x2F;www.rightmove.co.uk&#x2F;properties&#x2F;140100683#&#x2F;?channel=COM_LET" rel="nofollow">https:&#x2F;&#x2F;www.rightmove.co.uk&#x2F;properties&#x2F;140100683#&#x2F;?channel=C...</a><p>In terms of things like mixture of units, I appreciate you want to give in one unit but I think the things chosen are a bit strange. I&#x27;ve never seen anyone write &#x27;15070 grams&#x27;, it&#x27;d almost always be given as 1.507 kilograms.
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xico8 个月前
&gt; 1 KB = 1000 bytes<p>But standard is kB, from kilo prefix.
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Hadarai58 个月前
I&#x27;ve never seen Mtr, sqm or gr. Even as a child, I knew the short of those unit names.
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rightbyte8 个月前
Doesn&#x27;t seem right. I wonder why they claim cc and Å are &#x27;deprecated&#x27;.
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beAbU8 个月前
It would have been nice to know the risks of making each of these mistakes, since honestly I only found a few places where a mistake can have real negative consequences.<p>As with all things, context is king. I&#x27;m not going to be confused when my colleague asks me on slack if it&#x27;s OK to email me a 15mb (millibar) document - I know what they meant. Nor am I going to worry if it&#x27;s actually MiB vs MB, in this context it does not matter.<p>Also, although it probably be nice that we all standardised on the correct prefixes, literally nobody speaks in terms of gigameters or teragrams or whatever. We carry with us an internalisation of real world measurements, and use that to compute relativity when we read&#x2F;hear these numbers. It&#x27;s roughly 1000km from my home town to the coast, so if if the moon is roughly 400,000 km away, then that&#x27;s 400x the distance, pretty far. My car weighs roughly 1 ton, so Hafthor&#x27;s 501kg deadlift record is half my car - pretty impressive!
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Tor38 个月前
The most common error I see is &quot;kph&quot; which doesn&#x27;t even have any possible meaning. &#x27;kilos per hour&#x27; would in most places be taken as &quot;kilograms per hour&quot;. As in &quot;my weight increases by 3 kph when I visit McDonalds&quot;
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minetest20488 个月前
&gt; Use 1008 MJ monthly electrical energy consumption instead of 280 kW⋅h monthly electrical energy consumption<p>&gt; Avoid common non-SI units (suggested)... For serious science and engineering, SI units like metres per second should be used instead.<p>Yeah good luck with that... electrical power engineering speaks in kWh not MJ<p>&gt; 150 pJ gamma ray instead of 938 MeV gamma ray<p>Particle physicists will hate you if you take electron volts from them<p>While I&#x27;m at it, do you know that attaching suffix to SI unit is not allowed by SI &#x2F; IEC &#x2F;ISO? So abbreviating megawatt of thermal energy as MWth or decibel referred to 1 milliwatt of power as dBm is technically illegal:<p>&gt; &quot;When one gives the value of a quantity, it is incorrect to attach letters or other symbols to the unit in order to provide information about the quantity or its conditions of measurement. Instead, the letters or other symbols should be attached to the quantity.&quot;<p><a href="https:&#x2F;&#x2F;physics.nist.gov&#x2F;cuu&#x2F;pdf&#x2F;sp811.pdf" rel="nofollow">https:&#x2F;&#x2F;physics.nist.gov&#x2F;cuu&#x2F;pdf&#x2F;sp811.pdf</a><p>Yeah... all of my spectrum analyzers, signal generators, software-defined radios, antennas and RF interface control documentation is not ISO&#x2F;IEC compliant...
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kkfx8 个月前
few notes:<p>- &quot;Fuel consumption of 9.4 L &#x2F; 100 km&quot; is not &quot;the right form&quot; is a modern take, a more classic and still valid SI one is km&#x2F;l which is very similar to &quot;Fuel consumption of 9.4 LPK&quot;;<p>- &quot;25 {kW&#x2F;h,kW⋅h} to boil a tank of water&quot; are both strange forms, kWh is the common accepted way to express energy, no center dot multiplication needed;<p>- multiple prefix (vs power-of-10) and bare prefix are as well commonly accepted, I see no reasons to consider them wrong, while I can state formally wrong &quot;2 kilograms of rice&quot; because we do not measure the mass but the weight so it should be 1.961daN where deca-newtons are commonly used because 1 daN is roughly 1kgf commonly shortened to 1kg as we can commoly count 1kg[f] == 1 daN... For instance climbing equipment in the EU use daN to express maximum loads of connectors, ropes etc because of that;<p>- multiple quantities much depend on industry and conciseness, as we do not write units in table values but only in headers we tend not to write them three times in a row where from the context is clear what numbers means.<p>The biggest issue is makes habits changes. Actually we should not use km&#x2F;h as well, since for SI base unites are m&#x2F;s, but 3.6 is not an easy conversion like kgf&#x2F;daN, so in the EU we keep using km&#x2F;h, something meaningful in the past, when we go by horses and feet, but not much needed today.<p>Not to count software, where often recognize &quot;°C&quot; (two chars) BUT not ℃ (U+2103) and so on.
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iainmerrick8 个月前
I really appreciate this kind of plain and simple writeup, without getting into any &quot;falsehoods programmers believe about metric&quot;-type clickbait. Nice one.
tommiegannert8 个月前
&gt; 81 uL of catalyst -&gt; 81 μL of catalyst<p>Oh, interesting. NIST recommends &quot;L&quot;: <a href="https:&#x2F;&#x2F;www.nist.gov&#x2F;pml&#x2F;special-publication-811&#x2F;nist-guide-si-chapter-6-rules-and-style-conventions-printing-and-using" rel="nofollow">https:&#x2F;&#x2F;www.nist.gov&#x2F;pml&#x2F;special-publication-811&#x2F;nist-guide-...</a>
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ndsipa_pomu8 个月前
So, when using the kelvin temperature scale, it&#x27;s lower case when using &quot;kelvin&quot;, but uppercase when using the abbreviation &quot;K&quot;? That annoys me as kelvin is a name and even my phone wants to capitalise it.
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eNV258 个月前
A IB Diploma Physics textbook I had used a negative one exponent instead of a division symbol in units. This is not normal right?
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Timwi8 个月前
I love that they included a note on the pronunciation of kilometer. It drives me nuts how everyone says it wrong.
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kelnos8 个月前
This list strikes me as overly nitpicky. Certainly some of the bad example usage is a problem (e.g. mb vs. MB means two very different things, millibit vs. megabyte), but so much of this in practice just really doesn&#x27;t matter.<p>Sure, if I&#x27;m doing a bit of formal writing, I&#x27;m going to do things correctly. But I don&#x27;t see it as a problem for people to use odd abbreviations like &quot;mtrs&quot; or incorrectly pluralize as &quot;kms&quot; in informal writing. People will not have trouble knowing what you mean. No one is going to say things like &quot;I drove 3 megameters over the past couple weeks&quot;. (Reading some of the longer explanations below seems to indicate that the author is not just talking about formal writing.)<p>And even in formal writing, a few of these are bit much, like good luck getting people to stop using electron-volts in favor of picojoules.<p>This just seems silly; it&#x27;s hard to take this piece seriously, and all of the nitpicky arguments seriously undermine the (few) good arguments listed.
tkgally8 个月前
I thought this looked like good advice until I got to:<p>&gt; Mass&#x2F;weight distinction<p>&gt; Incorrect: He weighs 70 kg; Correct: His mass is 70 kg<p>&gt; Incorrect: She weighs 50 kg; Correct: She weighs 490 N on Earth<p>Really?! We’re not supposed to use kilograms to describe a person’s weight? And to describe someone’s weight, we have to use newtons and specify what planet they’re on? Good luck enforcing those rules.
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IsTom8 个月前
&gt; 6 tons of wheat 6000 kg of wheat<p>Why not 6 Mg of wheat?
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