Product review (1 stars): Comparing Extech 445815 to Acurite 00613
I always thought the readings seemed off on this device but it was the expert, right?  Anyway, I wanted a second moisture meter so I wouldn't need to keep taking this one back and forth between the bedroom and the living room.  So, I ordered the less expensive Acurite 00613 from Amazon ($10 versus $40), and inadvertently ordered two.  When they arrived, I planned to send one back.

 I  set up one of the Acurites, and its readings were significantly different from the Extech,  Which was right?  I didn't know, so I set up the second Acurite and it read exactly the same as the first one, which seemed like a pretty good indication that they were accurate and the Extech wasn't.  The Extech consistently reads humidity as 3-6 percent lower and temperature 1-3 degrees higher than the Acurites.  If I owned a fourth moisture meter of a different brand, and that one confirmed the Acurites, I would be completely convinced of their accuracy--but I don't have a fourth meter.

I did, however, compare the temperature readings on the moisture meters to our house thermostat, and the Accurites read exactly the same as the thermostat, while the Extech read higher.  Given the available evidence, I have to conclude that the Acurite meters are probably accurate while the Extech is not.  I am returning the Extech and keeping the two Accurites.  By the way, the Accurite is about one-half the size of the Extech: smaller display but less obtrusive unit.