The HD 21-TA-17 IAQ monitor is a laboratory device/portable device for the analysis of the indoor air quality, indoor air quality (IAQ). At the same time, the device measures the following values: Carbon dioxide (CO2), carbon monoxide (CO), atmospheric pressure, temperature, relative humidity. Thereby it calculates automatically: Dew Point, wet temperature, absolute humidity, mixing ratio, enthalpy. For closed rooms in which people reside. Kitchens, bathrooms, locker rooms and swimming pools are due to their high air humidity as well. The measurement of CO2 concentration also allows conclusions to be drawn about the chemical, physical and biological pollutants. The devices have a wide range of dot matrix display with a resolution of 160 x 160 points. Typical application area of the devices are: Measurement of indoor air quality (IAQ) and comfort conditions in schools, offices and closed rooms, analysis and investigation of the sick building syndrome (headache, nausea, irritation) and the resulting consequences, examination of the HVAC system efficiency (heating, ventilation and air-conditioning systems), examination of the indoor air quality in factories for the optimisation of the micro-climate and improvement of productivity, checks the building automation.This text is machine translated.