Overall I have had good success with this tester for the several years we've had it.  We pulled out a load of corn to sell to a local farmer last week, and our tester was reading low 20's, definitely higher than expected.  Repeated tests showed as high as 26%, or even "moisture above limit", and yes, it was on the "corn" setting.   Checked the corn at a local farm elevator, around 16.5%.  

Is the tester faulty, or has the calibration just randomly gone way askew and needs reset?