Each instrument has been tested for accuracy at 3 points on the scale for high, medium and low readings. The calibration and certification are done under ISO-9001 control. Housing is solid brass, polished and lacquered. The measurement of the temperature and relative humidity remains correct if the pressure goes up or down. This is confirmed for the pressure range of 600 to 1200 hPa (mbar) or 8.7 to 17.4 psi.