The Dräger Bio-check F is a colorimetric badge specifically designed to measure formaldehyde in the air. The badge is so sensitive that within a 2 hour sampling period, concentrations from 0.02 to 0.7 ppm can be measured. The measurements results of the Dräger Bio-check F are determined by comparing the discolouration of the badge with an enclosed set of colour standards. The badge comes complete with a uniquely shaped holder that clips easily onto the users clothing-or the device may be placed upright on a flat surface.