Although it has been discussed in the digest in the past, here is my
opinion on vacuum gauges:

The overall most reliable gauge is the water manometer.  It can be
difficult to read, unless a direct reading type is used, and can cause
damage if a water trap is not put between the gauge and vacuum source.
You can use a water gauge to test or calibrate a gauge in question,
but be sure to test for repeatability of measurements.

Other than that, the best affordable gauges are the Magnehelic types,
made by Dwyer.  They can be gotten from W. W. Grainger as well as any
company that sells HVAC supplies.  With the exception of precision
calibrated gauges, it is best to use a gauge at center scale for the
best accuracy.  Therefore you will probably want to have at least two
gauges to test vacuum levels in players, one for 0 to 100 water column
inches and one for about 0 to 10.  The two gauges can be hooked in
parallel, as the Magnehelic gauges are not bothered by pressures as
great as 15 psi, differential.  Two gauges will probably cost about $50
to $90 depending on where you buy them.

Another source for gauges is military surplus.  You can find gauges for
a few dollars that originally cost thousands.  You can even have them
recalibrated if you want to spend some more money, but for player work
repeatability is probably more important than an absurd degree of
precision.

Spencer Chase