Also, even though it might be stating the obvious, are the batteries new and are they the right type? I can't speak for other brands, but the Hygroset's are supposed to have silver oxide batteries (SR44/357) rather than the less expensive similarly sized alkaline (LR44/357a). When brand new, the batteries are about the same, but after a short period of use, they start performing differently. While silver cells will stay basically constant until right before they croak, alkaline cells start slowly dropping in voltage from the word go. This could be causing reading errors/fluctuation between the units.
