The method involves utilizing a fabric-new gas detector (4) as normal. A reference gas sensor of a test device (1) is calibrated by the detector to measure concentration of reference gas. Another gas detector (3) to be calibrated is calibrated by the gas sensor. Calibration electronics (11) is communicated with the former gas detector and/or a control center (17). An operating mode is switched between a mode for calibrating the test device and a mode for calibrating the latter gas detector using the calibration electronics and a switch. An independent claim is also included for a test device for calibrating a gas detector.
