Product review (3 stars): HARD TO CALIBRATE
This unit is very hard to calibrate.  The screw adjustment did not move the result.  Calibration takes 6-7 attempts.  Finally got a consistent result in calibration.  The customer service was non existent.  I believe they use quality control to separate the units selling those that pass for a higher price then taking the marginal units and selling them for 50 bucks.  I would not buy this unit again and still contemplating returning it and trying a different manufacturer.