Product review (5 stars): I saw it climb
I have no way of checking the accuracy, BUT, that said, When I put the battery in and let it sit @ an hour -the humidity read 22 DRY.  I checked the humidifier on the furnace and found it was set way too low; almost off.  I adjusted the humidifier upward and watched the TP50 climb steadily to 36 over a two day period.  I am satisfied. It did help me.