Testo 552 Digital Micron Vacuum Gauge with Bluetooth is designed with a unique absolute pressure that requires no maintenance and gives accurate vacuum readings for working on refrigeration and AC systems. The Testo 552 digital micron gauge also measures H2O evaporation temperature, has an optical alarm that activates when set pressure limit values are exceeded, connects to your smartphone or tablet device via Bluetooth, measures down to 1 micron, and more.