It's never a good idea to guess with measurements, that's what measuring tools are for. There's no cord to restrict you, just make sure you've charged the battery.
From Amazon
Flir MR160 Imaging Moisture Meter
Acme Tools
FLIR Imaging Moisture Meter with IGM
Conrad Electronic
Moisture meter FLIR MR 160 Building moisture reading range 0 up to 100 vol% Built-in IR camera