Comment by delta_p_delta_x | Hacker News Reader

Comment by delta_p_delta_x | Hacker News Reader

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delta_p_delta_x

People have used all sorts of abbreviations for the SI prefixes and SI units for as long as I can remember. I want to ask—are people not taught this in school? I had multiple introductions and revisions of the SI units and SI prefixes in secondary school, pre-university, and university, and every time, a wrong prefix or a wrong symbol was penalised by half a mark per question. I had classmates who mixed them up regularly and lost something like seven marks each time. They learnt very quickly not to, as those seven marks could make one or two grades' difference.

As someone who champions sole use of the SI units, this annoys me to no end.

I've seen things like 'kgs', 'gm', 'gms', 'mtr', 'mt', 'K' instead of 'k' (note capitals) for 'kilo-', mixing 'm' and 'M' (which are supposed to mean 'milli-' and 'mega-' respectively), usage of 'u' instead of 'μ' for 'micro-' (the one exception I will concede is 'mc' in the medical field, because people apparently confused 'μ' and 'm' which results in a 1000× over/underdose), and don't bother with the degree symbol (Alt+numpad 0176 on Windows, Option-Shift-8 on macOS) for °C, or use °K for kelvins (there is no degree, as it is an absolute scale and not relative to anything else, unlike the Celsius/centigrade and Fahrenheit scales), and so many other typographical errors.

https://www.nayuki.io/page/common-mistakes-when-using-the-me...

I love this, thanks so much for writing it! I'm writing a blog post on metrication and this will be a super-useful resource for the sort of pedantry I intend to engage in.

Then see my point about the UK/metric/Imperial. ;-)

Incidentally, in that link there's a very common example of bad usage namely the volt/voltage. 120V is shown as bad usage and 120 V good. One sees the former usage on machines, appliances, in printed material etc. so often that it's almost a de facto standard.

I'm inconsistent in my use too, one time I'll include the space at other times not.

> are people not taught this in school?

I agree about standardization, but I think this framing comes off as lacking empathy. Plenty of folks either

- Avoided the topic in school or put all their effort into other subjects

- Didn’t learn this in school—there are a wide variety of education systems across all the decades and distances that folks on this site may have grown up in

- Learned this in school, but a lifetime ago, and haven’t had a reason to revisit it. At a certain distance, your life experience and work experience massively overshadow what you learned in school.

Forgive the inference, but based on your recall of specific grading policies I would guess that your time in school is still near to you, or at least very important. It’s not that way for everyone.

(I am of course doggedly accurate with my unit abbreviations.)

[edit: list formatting]

"People have used all sorts of abbreviations for the SI prefixes and SI units for as long as I can remember."

In the US that is, not in metric counties that use SI by default.

For those in the US (and to a lesser extent the UK) there are multiple metric systems. The other notable system that's still in use is the cgs (centimetre–gram–second) system.

'cgs units' are still used in some areas notably physics as they can make calculations easier, there they're called Gaussian-cgs units.

Incidentally, often, as here, 'cgs' is in lowercase to reflect the case of the units' abbreviations. That said, the uppercase abbreviation is also often used. For instance, as I typed this my browser kept correcting the lowercase to 'CGS'.

> In the US that is, not in metric counties that use the SI system by default.

India which metricated in the late 1950s is still a big (ab)user of poor SI symbolism. A lot of the 'cms', 'gms', 'cc', 'kgs', etc come from Indian writers and Indian publications (case in point: the article in this thread).

> The other notable system that's still in use is the cgs (centimetre–gram–second) system.

> 'cgs units' are still used in some areas notably physics as they can make calculations easier, there they're called Gaussian-cgs units.

I'm not sure they're used all that much—I was under the impression most CGS units fell out of favour as MKS and eventually SI took over. I was an RA at my physics department for a while and we used SI as much as we could. Some specialisations use a certain form of natural units (like geometrised units in general relativity), but by and large SI dominated.

Right, there are offenders everywhere but the chief offender is the US by far (many don't have a clue about SI let alone metric, ask an American what 20°C is in Fahrenheit and they've no idea).

The UK is also troublesome in that whilst supposedly a metric country Imperial is still commonplace. For example, there's widespread use of antiquated units like the 'stone' (14 pounds)†, even BBC medical programs still regularly use the term.

Re Gaussian/cgs, in physics it's still widely used especially in field theory/Maxwell, SR (Special Relatively), etc. because in charge calculations and such involving permeability, permittivity, speed of light certain terms can be restated as 1 instead of their actual SI values.

Personally, I understand why this is done but from my perspective it's confusing if not misleading for reasons well outside this discussion (but who am I to argue with those more learned than me?). This Wiki provides justification of sorts (see Unit of charge): https://en.m.wikipedia.org/wiki/Gaussian_units.

† In Australia where I am, only people of my generation who've been around for decades would even know what a 'stone' was. Anyone born after say the mid 1970s would likely think you're talking about a rock. Trouble is, we see BBC/UK programs here. Fact is the UK is oblivious to the problem or it'd first correct its exports.

Why would your average American need to know what 20°C is in Fahrenheit? Very few people use Celsius here. All our appliances use Fahrenheit, weather reports use Fahrenheit, our recipes use Fahrenheit, and for science and physics we use Kelvin.

Honorable mention for "cc", which stands for "cubic centimeter" which is exactly equal to 1 ml. I can't find any logic to explain why cc is used in some contexts and ml in others.

And the SI for that is... cm³.

The problem is old habits die hard and to be (or appear) to be consistent then an official designation can be unwieldy, as here.

I simply cannot remember when I last saw cm³ but cc and ml are everywhere including on commercial chemical reagent bottles etc.

The same nomenclature problem is all over chemistry too, the preferred IUPAC name for say isopropyl alcohol is propan-2-ol, and the preferred name for acetone is propan-2-one (systematic 2-Propanone). I can't say I've ever heard anyone ask me to pass them the bottle of propan-2-one, it's just not done (not in my world anyway).

If there's a choice between an awkward or simpler term then the simpler one wins out every time.

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