• The return value is 2 bytes wide unsigned CO2 concentration value, the unit is 1 ppm, the resolution is 1 ppm, and the theoretical range is from 0 ppm to 32,767 ppm. Value 0x8000 (i.e. 32,768 ppm) specifies a sensor error. Greater values are not used.
• FRC 1-byte: FRC return value uses 16 ppm resolution. Return value F = ( CO2 / 16 ) + 4 so CO2 = ( F ‑ 4 ) * 16 (i.e. 4 is 0 ppm, 255 is 4,016 ppm). Range is from 0 ppm to 4,016 ppm. When the value is above this range, FRC error value is returned.
• FRC 2-byte: FRC return value is CO2 value +4 (i.e. 0x03EC=1,004 is 1,000 ppm).