My Oasis XL plus reads about 4% high, but I read from a cheapo walmart hygro that I have salt tested. I have the Oasis set at 63%, and have a pound of 65% beads to do most of the work. My cooler holds steady at 66%.

I recommend using only one hygro that has been salt calibrated.. a little bit of math, and a lot of patience.

Or... Just get some beads