Product review (3 stars): It's Okay I Guess
Ordered three units from three brands and salt tested an analog hygrometer also for a control subject. This unit was off by about 3-6% humidity, depending on the room/conditions.  It doesn't appear that there is any way to calibrate the unit either, aside from just doing a hard reset.
 Which doesn't fix the hygrometric inaccuracy.  So you're stuck with that slight "offness".

Temperature, however, is accurate to within about .5-.75 degree F.  Real close.

So I'm giving this three stars.  It's okay.  If you need better accuracy, get an analog and do the salt test deal.