Yep, gotta calibrate the hygrometer. Fill a plastic bottle cap with salt. Add just enough water to completely wet the salt. No more. Place the cap and your hygro in a ziploc bag for at least 8 hours. The relative humidity inside the bag is now 75%. If your hygro reads 81%, it is 6% high. Hygrometers are inaccurate, in all cases, unless you paid several hundred dollars for it. Just do the math when you're done and you know what the deal is. After you've done all that, get the beads. They rule!