Product review (2 stars): I purchased this Extech RHM15 and an Extech 445703 (larger) ...
I purchased this Extech RHM15 and an Extech 445703 (larger) hydro-thermometer at the same time.  The two agree on temperatures but this one is about 6-7 points high on humidity (about a 20% difference).  I had planned to use the larger unit in the room and the smaller in a guitar case but I'm not sure I trust it...