Andy adds :

One more thing.


"Eric" sent me an Email telling me that he worked for a gas company
that used a little
tube of clear plastic to determing the pressure. It was partially
filled with water and
one end open and the other connected to the pressurized line. A simple
ruler, in inches,
was used to determine the pressure......

Sure... That's called a "manometer". If you mount it on a nice
stainless steel plate and
put a calibrated ruler on it, you can buy one for between 10 and 1000
dollars, depending
on the quality. Personally, I use the little plastic tube and my kid's
ruler, since I don't
need calibration to 4 decimal places (grin).

For very low pressures, you can't beat this method.

By the way, the LARGER the diameter of the tube, the higher the
accuracy. It has
to do with capillary action...... If you have a half inch diameter,
it's pretty good......

As an out of class assignment, do a google search on "water levels",
which is a
way to us a very long plastic tube to determine that a very long piece
of anything
is level...... This stuff gets interesting when you start applying
these principles to
stuff you might need to do......