Bill, I bought a 12 pack of those hygrometers and they were terrible. I put all of them in a container with moistened salt (which should read 75%). Most of them were over 10% off.
That's when I decided to try Grove bags, and so happy I did. No burping , no bovedas, and no hygrometers needed. Here's a readout for 9 oz of Jenny, a Purple Haze, curing in a 1 lb grove bag over the last month.
The best part is that the bags keep more terpenes too. Overall, they cost less than canning jar+boveda+hygrometer. I love my Grove bags.