I bought a vacuum gauge from Player Piano Co. some time ago for about
$70.00 (US).  It gives readings from 1-60 inches of water.  While using
it I found that it would give false readings when measuring values less
than 5 inches.  If the vacuum went up or down by 1/2 to 1 inches, the
needle would not register the change.  I don't know if this is because
the gauge is bad or just cheap.  There isn't any name on it to
reference it to a manufacture.  I only use it for getting ball park
measurements that don't need the accuracy.

I now use a cheap water gauge instead of a mechanical one for fine
measurements.  It is similar to the one that Craig Brougher talks about
in The Orchestrion Builder's Manual.  It is very accurate but you must
protect your vacuum source from sucking up water if the level is over
70" of vacuum.

Buy a 6- or 7-foot piece of acrylic tubing from a plastics supply house
($10-$15).  The inside diameter should be 1\4 inch with an O.D.  of at
least 1\2 inch.  Take an old metal tape measure (like the one a wood
carpenter would use) and attach it to the side of the acrylic tubing.
Run it along the entire length.  I use twist ties and rubber bands.
The excess tape can be run back down to the floor or cut off so there
isn't excess weight at the top of the acrylic tube.  The rubber bands
allow the tape ruler to slide up and down on the outside of the tubing
so it can be calibrated.

Now take a long length of tracker bar tubing and push it inside one end
of the acrylic tube.  This is the top of the gauge.  It should fit
snugly without any air leaks.  Take a large wash tub or cake pan and
fill it with water.  It MUST be fairly large so that the water in the
pan will not move down very much when the water is sucked up into the
plastic tube.  Place the bottom end of the acrylic tube in the tub of
water and figure out some way to get the plastic tube to stay vertical.

Now calibrate the gauge by moving the bottom of the measuring tape so
that it just touches the top of the water.  Test the air tightness of
the gauge by sucking on the end of the tracker bar tubing and then
blocking it with your tongue.  If the water level in the tube doesn't
move down, you are now ready to start testing.

To read the gauge, you measure how high the water rises in the plastic
tube.  If the water goes up 3 inches, you have a vacuum of 3 inches of
water.

Remember: *If the vacuum level goes above the rated value of your
gauge, water will enter into the testing area and cause damage.*

Pete Knobloch (Tempe AZ)