No need to use tables or make calculations with this sling psychrometer for humidity monitoring. Spirit-filled thermometer and holder telescopes into swivel handle. Sliding scale converts wet and drybulb readings into relative humidity. The 20° to 120°F thermometer with 1°F scale divisions are protected by a strong plastic frame with built-in water reservoir to saturate wick. Feature magnifying front, deeply etched numerals, and thin bulb giving fast thermal response.