wrote in message
...
On Tue, 17 Mar 2015 18:44:46 -0400, Bob Engelhardt
wrote:

I'm pretty sure they measure temperature and pressure to arrive at
the
volume of gas in the cylinder. But since the temperature may be
different when you pick up the cylinder the pressure will vary. So
on
a cold day there is less pressure, a hot day more pressure, but the
same volume of gas in all cylinders. Acetylene cylinders show a very
wide pressure swing with changing temperature. That's why it is hard
to know how much gas is really left in the acetylene cylinder unless
you know both temp and pressure.
Eric

The little I've seen suggests they hook the cylinder to a hose from
the manifold and just leave it for a while, hopefully long enough for
it to fill and cool to loading dock temperature. It's hard enough to
get a good answer on welding from them, I won't even try physics or
chemistry.

-jsw