Extech 406800-NIST- NIST Calibration Certificate Manometer Differential Pressure features: Measures Gauge/Differential Pressure from 0 to 138.5 inH2O (inches of water); 11 selectable units with Max/Min recording and Relative time stamp; Compensated temperature range 32 to 122°F (0-50°C); Large LCD display with backlighting; Zero function for offset correction or measurement; Built-in RS-232 interface.