Product review (5 stars): Precision Instrument
I bought two of the Extech 445815 at the same time.  The temperature readings match exactly.  There was 2% variation in the
relative humidity reading.  Fortunately, I also bought the Boveda One-Step Hygrometer Calibration kit.  One hygrometer was exactly right, the other was calibrated higher so it matched.  I am very pleased with the outcome of this purchase.