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Comment by nesadi | Hacker News Reader

> that SI is generally used for engineering

Except when it isn't? Are you telling me SI is used in engineering everywhere in the US? I've heard too many stories (especially accidents) to believe that in any way.

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Nope. Hence generally. I haven't made a study of it but I assume Imperial units are more common in civil engineering and other areas that converge with local construction and building trades. Metric is pretty standard in my experience more broadly. (Note also that the better known examples of unit conversion accidents are pretty old as far as I know.)

don't they still use pounds per square inch ?

Now, in Europe (excluding the UK) they also still use some weird units from the past. Calories for example, and horse (!!) power.

A calorie was originally defined as as the amount of heat required at a pressure of 1 standard atmosphere to raise the temperature of 1 gram of water 1° Celsius.

But you're right that is sort of a weird unit from the past insofar as it's related to the SI system but isn't formally part of it. (It's basically now defined by its ratio to joules.)

Adding: There are a number of measurements that aren't necessarily obviously related but are actually the same thing in terms of units. Heat, work, and energy are all newton meters or kg m^2/sec^2 in SI units.

PSI is very commonplace though I'm not in a field where I use it in an engineering way. (I actually had to think for a second to come up with the SI equivalent.)

Pounds are one of the real bugbears of imperial in mechanical engineering with lb-f and slugs (i.e. "pounds" conflates mass and weight). Always hated that. I'd convert things to metric and then convert back when I had to work in Imperial.

And I still hear stones from time to time in the UK if you really want archaic.

Yeah, a lot of people in the UK use stones for weight. Even young people in my experience.

We still use PSI for tyre pressures in UK, probably some other things too.

They're given in N/m^2, but all the petrol station machines are in PSI, probably because the numbers just fall better.

I thought they were given in bars instead of N/m^2.

Aye, could be. Just checked my manual and they're in KPa and Bar.

On the UK railways, I think I'm right in saying that the only place imperial units are used is in measuring the curvature of track, which involves chains.

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