HOWHI VACUUM GAUGE is a digital vacuum gauge for obtaining accurate vacuum measurements during filling refrigerants. It features a professional vacuum sensor to precisely test vacuum. The evacuation of an HVAC and refrigeration system is to evacuate the air and moisture in the system, which, if mixed with refrigerants, may produce an acidic chemical reaction, causing damages to the system in long term. Generally, a system vacuum should be below 700 microns so that the moisture in the system can be effectively reduced. The best vacuum is 300 micron. Common refrigerants cannot meet this requirement. HOWHI is used to test system leak and discern vacuum pump quality. Specifications Range: 0-10000pa/0~100.00mBar 0-75.000mmHg, 0~75000Micron Operating temperature: 0~50 Degree C (32~122 Degree F) Measurement accuracy: 2~100pa: ± Percent of reading (at 20 Degree C) Sensor: 1x Pirani sensor Backlight time: 20 seconds Buzzer: 90 decibel volume, automatically shut down after 10s Weight: about 125g (without batteries) Scope of application: atmospheric environment (not used for measurement in other environments containing refrigerants) Packing: 1x vacuum gauge 1x storage box 1x extension interface