Applications check for proper pressure in Pneumatic systems check supply gas pressures check for proper pressures in clean rooms check industrial HVAC systems check operation of industrial pressure switches same as 645 (42500-24) but with 1?4" NPT) to 1/4" barb fittings, 2 stainless steel compression fittings, carrying case, and protective boot measure pressure of air and natural gas . 655L measures pressure of non-corrosive water/liquid applications . Rugged extruded aluminum housing . Measure positive differential pressure . Push button zero for Altitude correction . Seven selectable units of measure to choose from: mmHg, inhg, kPa, mbar, psi, Inh20, and Mmh20 . Backlight with auto shut off after 10 seconds . Auto shut off after 30 minutes (except REC mode) to save battery life . Easy-to-read LCD . Record function stores maximum and minimum readings . 3-Year limited warranty . Data hold to freeze reading on LCD.