I don't know about enforcement in Michigan, but the commercial grade moisture testers are rated accurate to .4%. I assume this is ±.4% and not a range of ±.2%

(edit) Found it. Michigan weights & measures law 2011 excerpt:

"Weights and measures means weights and measures of every kind, instruments and devices for weighing and measuring, grain moisture meters, and any appliances and accessories associated with any or all of those instruments and devices."

So yes, Michigan is supposed to be checking them.