Humidity Range: 0 to 100%RH. Humidity Accuracy: +/- 5%RH between 40 and 80%RH, otherwise +/-9%RH. The reset maximum and minimum pointers - first turn the red pointer anti-clockwise using the larger nut until it just touches the black point and then turn the blue pointer clockwise using the smaller nut until it too, just touches the black pointer.
eBay