TPI 645 - Dual Input Differential Manometer Differential input with + 29 PSI range. 4 digit dual line with backlight Stabilizes display when measuring fluctuating pressuresDual Differential Input Manometer with +- 29 psi range and 0.1 psi resolution. Seven units of pressure: inH2O, mbar, KPa, PSI, mH2O, mmHg, inHg, Auto power off, Record/Min/Max, Backlight display, Zero function, Trim mode to stabilize readings.Features & Benefits Auto ranging - Provides high resolution & accuracy at low pressures where it is needed Auto Power Off - Powers off after 30 minutes to conserve battery life. Trim Mode - Smoothing function to stabilize erratic readings. It displays the average value of 4 values previously measured. Zero function - Provides immediate push-button zeroing for Speed and accuracy. Record Max/Min - Enables long term testing of pressure systems for leaks Hold - Enables the user to freeze the display reading, when working in cramped working conditions, when the display is not visible. Units - Change the display value in anyone of the following engineering units. kPa, PSI, inHg, mmHg, inH20, mH20 and mbar.