Gauges are especially ideal for accurately measuring low pressures, either positive or negative (vacuum). Two legs contain liquid levels which are read up and down from zero on the scale. Using water as the indicating fluid a pressure drop or increase of 0.0576 ounces will change the indicating level 0.1"". Using red oil 0.1"" change in level indicates a pressure change of 0.464 ounces. With mercury 0.1"" equals a change of 0.7856 ounces or 0.0491 pounds per square inch. Made for operating at pressures up to 250 psi. Head of manometer is a solid semi-steel casing, tapped with 1/4"" IPS threads for direct line connections. Supplied without indicating fluid.