Hi Rabc,
Mine is an old faithfull and says fai detdamp on it.
It is handheld and runs off hearing aid batteries. I check my motorhome once a year or so and it is always 0.1% or below!
I also use it occasionally at work to see how dry plaster is on walls before tiling, I don't know how accurate the reading is but I use it as a guide with confidence.
Rolling on and enjoying life on the road