Like the guys say, they are of limited use, I bought one just as a check, it's handy now and again, I tended to use it on the off cut wood from the end of a stave if I'm not sure how it's doing or if I was seasoning a stave on a radiator. But now I rely on feel mostly.
I try not to fight the climate too much, and I prbably have a slightly higher moisture content than ideal (Englan id pretty humid generally) but I'd rather have a bit of set than a snapped bow).
The one I had came with a built in calibtation check which gives a defined reading when placed across the pins.
Del