The ventilated type of hygrometer gives greater accuracy for humidity demonstrations and is particularly useful for measuring local differences in humidity. There are two thermometers mounted inside a case, fully enclosed to prevent breakage, one dry and other having a wick dipping into a water reservoir at the end of the frame to keep it wet during long periods of non-use. The thermometers are stem engraved with lens fronts for easy reading, range -5 to 50 × 0.5°C. Includes humidity and temperature conversion chart.