Vacuum gauges, like pressure gauges, come a varity of ranges.
You can get gauges with a full range display of anywhere from a few inches water column (typically used to measure the draft in a flue, or the suction casued by a dirty filter in an HVAC system) to full vacuum (approx -15 psig or 0 psia).
For reference, 28 inches water column is about equal to 1 psi, so a 3" or 4" water column gauge (fairly common in HVAC) is not much pressure.
In the more than you care to know department, the low range gauges are typically U-Tube manometers (or some variation on a U-tube) or a bellows activated mechanism instead of the bourdon (?sp)tube used on higher range gauges.
Ugly