For indoor air quality and comfort, the measurement of the carbon dioxide content in the indoor air is crucial. To obtain precise results quickly, you need a suitable measuring instrument. The compact CO? measuring instrument testo 535 with practical App connection allows you to carry out this important measurement easily and efficiently - and thus ensure comfort and a healthy indoor climate. Thanks to the long-term stable infrared sensor technology, the measured values are reproducible and comparable even over longer periods of time. Ideal for recurring comparative measurements. Here, you are also supported by the time and point averaging directly in the measuring instrument. By the way, the testo Smart App displays the measured values as a table or graph, stores the results and documents them. This not only makes it easy to configure the measuring instrument individually - the App also turns your smartphone into a second display!