Mason's Hygrometer, Sper Scientific, Mfr#: 736740

Measure Humidity – Mason’s Hygrometer – Red Liquid One thermometer bulb is kept constantly wet by a siphon reservoir while the other gives a dry temperature reading. Humidity is obtained by comparing the two readings on the enclosed chart. The red liquid masons hygrometer uses a safe and easy to read red liquid in place of the usual mercury. Dual scales of -10/50 degrees C and 10/120 degrees F. Downloads Instruction Manual Comparison Chart Comparison Chart