Acu-Rite 00613 Indoor Humidity Monitor

Features:

Displays indoor humidity and temperature
Displays Lo / OK / Hi comfort level icon
Keeps track of daily high/low temperature and humidity
Uses 1 AA (1.5V) alkaline battery (not included) 
Main unit dimensions:  3" X 2 1/2" X 1 1/4" inches
Includes magnetic back for easy mounting to metal surfaces
Includes tilt stand for easy display on tables and desks

This product can help you monitor the effectiveness of your dehumidifier and/or humidifier.