Cole-Parmer 22014 Psychrometer, 10 to 120F, 10 to 100% RH/

What's included: one 2-oz water bottle, psychrometric slide rule, tables, chart, extra lamp, extra wicking material, and carrying case.

Psychrometers measure relative humidity without agitation. To use, turn on the fan and let it run for 1 1/2 to 2 minutes. Then, subtract wet bulb reading from dry bulb reading and use the included slide rule and tables to calculate the RH. Fan is powered by three size D batteries (order separately).