NDIR method principal for CO2 ( Carbon dioxide ) measurement available for long term operation. High repeatability and high accuracy. Separate probe easy operation and convenient for remote measurement CO2 function with alarm setting Large S-TN LCD high contrast easy readout. Data hold function for freezing the desired value on display. Records maximum and minimum readings with Recall RS232/USB computer interface. Microprocessor circuit assures maximum possible accuracy provides special functions and features. Heavy duty & compact housing with hard carrying case designed for easy carry out & operation. Power supply from batteries or DC 9V adapter.