- -123. OPERATIONDuring turning on, the following message is displayed for about 10 seconds:Model HD21ABE17Indoor Air QualityFirm.Ver.=01.00In addition to the Delta Ohm logo the instrument code and the firmware version are displayed.After about 10 seconds, the measurements will appear on the display:HD21ABEHD21ABE2010/02/10 08:00:00 CO 2 : Carbon DioxideCarbon Dioxide CO: Carbon MonoxideCO 2600 Patm: Atmospheric PressureppmCO 0 ppmPatm 1000 hPaHD21ABE17HD21ABE172010/02/10 08:00:00 CO 2 : Carbon DioxideCarbon Dioxide CO: Carbon MonoxideCO 2600 Patm: Atmospheric Pressureppm RH: Relative HumidityCO 0 ppm T: TemperaturePatm 1000 hPaRH 25.0 %T 17.0 °C