The Model 116 Whirling Hygrometers use a manual technique to measure Relative Humidity (RH) and dew-point. These instruments consist of two thermometers, the bulb of one being covered by a wick. The wick is saturated with water and the hygrometer whirled for about 90 seconds. RH and dew-point are then calculated from the wet and dry bulb temperature readings using the guide or the Elcometer 114 Dewpoint Calculator.