Re: SI &c.

[Mark Sylvester <msylvest@SPIN.IT>]

At 11:37 29/08/99 -0700, Daniel Schroeder wrote:
<snip>
> Leigh:  What unit of (barometric) pressure is used in weather reports
> up there?  (My guess is bars or millibars, like my bicycle tire gauge,
> but official SI would require pascals or kilopascals.)
>
> -dan

tyre pressure units form a whole field on their own. I grew up in S. Africa
with "psi", which became "metricated" (what a word!) in due course, but
when I came to Italy I was bemused to find "kg per square cm". When I
criticised this beast in class, my Italian students told me that this unit
was the legal one, and one was not allowed to use pascals commercially! I
never found out if this was really the case.

Interestingly, though, "converting" to 9.8 N cm^-2 gives 98 kPa, which is
close enough to 100 kPa (1 bar), which is close enough to 1 atmosphere
(101.4 kPa), so for tyre pressures the three units are interchangeable,
which links nicely to the thread on significant digits.

Mark
Mark Sylvester
United World College of the Adriatic
34013 Duino TS
Italy.
msylvest@spin.it
tel: +39 040 3739 255