What is a hygrometer and how is it calibrated?
A hygrometer indicates the moisture in the prevailing surroundings, a useful instrument in the home. Please note that the hygroscopic element of the modern hygrometer coil declines in accuracy over time. To recalibrate the instrument place the unit on a platform in a vessel that contains water. Place a lid over the top of the vessel and leave it to stand for 6 hours. Immediately when opening the vessel set the hygrometer indicator to 95% by rotating the coil casing visible from the back using a small screwdriver. After a few hours the hygrometer will revert to the correct reading for its surrounding conditions. Note that if fitted to a barometer the hygrometer should be removed before carrying out this procedure and must not be immersed in the water.
