Re: off topic Question of the day..
On Fri 15 Jul 2016 at 22:48:11 (-0500), John Hasler wrote:
> Dennis writes:
> > BTW: one inch now equals 2.54 cm *exactly*, in case you haven't been
> > keeping up! (Used to be approx 2.54 cm.) This is what I mean by
> > arbitrary. Don't like the conversion ratio? Then just change it!
>
> It wasn't a change in conversion ratio. It was change in definition.
> Originally US length measures were defined by a physical standard
> derived from the British yard such that the inch worked out to close to
> 2.54cm. In 1893 the inch was defined as 2.54cm
Close, but no ciger. The 1866-07-28 length of the US yard was
preserved at 3600÷3937 of the metre. What changed in 1893 was
the adoption of the International Standard Metre (21 and 27
were the ones they received) as the prototype.
The change to inch=2.54cm came much later (1959-07-01) and was
actually expressed as one yard = 0.9144 of the metre. The old foot,
the US Survey foot, is still used by the National Geodetic Survey
for the publication of heights. Some states still publish their
State Plane Coordinates in feet (provided to them by NGS in metres)
and are at liberty to use either type of foot.
> and BIPM-supplied meter
> and kilogram standards became the official US measurement standards. It
> took until 1930 for the Brits to catch up.
Who was first is of little real interest. What's difficult to argue
against is that the Brits have pretty well gone metric with a few
exceptions like distances between towns, beer glasses, and the
freedom to sell milk in pints or litres. The Americans have not.
Even scientists convert their statements into customary units when
they commnicate with the public. And, of course, the most notorious
example of using the wrong units was the $125-million loss of the
Mars Climate Orbiter in 1989 because someone was using pounds-force
instead of Newtons.
At school in the 60s, we used the poundal instead of the
pound-force (on the rare occasions we used Imperial units).
Perhaps this was because the staff were unwilling to teach a
class of children to measure mass in slugs.
Cheers,
David.
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