VOLTCRAFT 2383436 Operating Instructions Manual page 37

Before calibration, run the device for at least 20 minutes with
windows open or in an outdoor environment using a portable
battery source to reach an atmosphere with 400 ppm CO2. Wait
until the CO2 reading is stable and follow the above steps for
calibration. After calibration, wait 10 minutes before normal use.
5 TEMP units
Press
Use this function to toggle between Celsius (°C) and Fahrenheit
(°F) for the temperature display.
6 ADV
Press
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