I recently bought a Lignometer SDM pinless moisture meter.

What's the expected accuracy of these things? I tried it on my kitchen cupboard doors, and got readings from 7.4% to 9.1%. (set in 1/4 inch depth mode, doors open).  Is that a normal spread? I realize not all the pieces are from the same tree, and maybe there could be differences in equilibrium moisture from sample to sample.

(at the moment, just using it for some new lumber across time to see when it stops equalizing)