JB's Digital Vacuum Gauge reads vacuum in 7 international units: Microns, PSIA, InHg, mBars, Pascals, Torr, and mTorr. The DV-22N has a micron range of 20 to 9,000 Microns. It is a good idea to attach the micron gauge to the vacuum pump before evacuation to make sure the pump pulls down to at least 50 microns. If it doesn't, your pump is contaminated and the oil should be changed. A compound gauge only indicates that a vacuum is being produced, but does not tell you if moisture or acids are still in the system. The DV-22N, however, is the only tool to accurately read the low pressure produced when evacuation/ dehydration is complete.