Hacker News Reader

Comment by diarrhea | Hacker News Reader

"mb" is not millibar; "mbar" is.

Maybe not officially, but in practice that's how it's used:

The unit's official symbol is bar; the earlier symbol b is now deprecated and conflicts with the use of b denoting the unit barn, but it is still encountered, especially as mb (rather than the proper mbar) to denote the millibar.

https://en.wikipedia.org/wiki/Bar_(unit)

Yeah, in general, there are many, many "unit collisions" that can really only be exactly interpreted from context. I think it would be great if everyone started using bracket notation (or similar) for prefixes. E.g. [k]B [Mi]B This is the convention used in pqm.js and it works really well. this would go a long way toward units that can be accurately read by a computer.

But is the SI system ambiguous? I almost never have to think about prefix v unit, it is always quite clear. Of course, strange combinations can occur (MNm - Meganewtonmeter as an example perhaps), but even those are unambiguous on second thought.

Collisions seem to be most prevalent in "IT" units or for improper SI usage. But maybe the latter is really the reason for the former in this case: if people separated SI and other units properly for IT units, it seems to be it would also be perfectly fine (but like me, a lot of people seem to have no idea of the correct definitions).

If you are strictly sticking to the SI system of units, you should be fine. However, some of us work in industries and countries (You know where) that don't fully embrace SI, and mixing other systems with SI is common.

> some of us work in industries and countries (You know where) that don't fully embrace SI, and mixing other systems with SI is common

That's actually pretty much everywhere since metric and SI are two different things. Use of the litre is deprecated under SI.

Pressure measurements/specifications are part of my daily work. I have never seen "b" referring to bar, also not in any of the many American (imperial) papers I have come across. So this is either properly old usage indeed, or very specific to certain regions or industries (like usage of relative v absolute pressure). Or Wikipedia being properly pedantic.

Reply on news.ycombinator.com