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.The Model 116A (spirit) and Model 116B (mercury) Whirling Hygrometers are available in either Celsius or Fahrenheit scales. A guide for Relative Humidity (RH) calculation is supplied with the instruments. Use the 116B mercury filled thermometer whirling hygrometer in accordance with BS 2842 test methods.Lightweight & compact instruments - easy to use Manual operation - no power supply required