Review on EEEKit 6-Pack Digital Hygrometer Thermometer LCD Monitor - Indoor Outdoor Humidity Meter Gauge for Humidifiers Dehumidifiers, Greenhouse, Basement, Babyroom - Black Round Design, Fahrenheit/Celsius Measurement by Jermall Meredith

For those who don't know, HVAC vacuum pumps are used to remove air and MOISTURE. I have a 5 gallon vacuum chamber that I put them in and they have NEVER dropped below 17%. I pumped the chamber down to a 1000 micron vacuum and left it there for a couple of days where the water boils at less than six degrees and is removed from the chamber. I restarted the pump several times throughout the day while maintaining a high vacuum. There is NO humidity in the chamber, but it is 17-18%. TOTALLY CRAZY. Seriously, DO NOT waste your money. Also, HALF of them had dead batteries, forcing me to buy a replacement. you have been warned