No off the shelf hygrometer is accurate. They don't use good sensors, but what would you expect for $10.

If your hygrometer can be adjusted to match 75 during a salt test then there may be hope.

If you want to know with accuracy, the EXTech pen is the way to go. I calibrate all my desktops with it by getting the h% where I want it then noting what the cheapo hygrometer reads to know how much they are off.

Almost all Radio Shack ones have been 4% off.

I have tried many different brands. They all suck for accuracy.

Only the Pen, and the units that come with a cabinet (Aristocrat, Arlin Liss, Avallo...etc) are accurate.

The only thing I have not tested of late are the new cigar oasis digital models.