These have to be the least accurate things I have ever seen.
The rectangular one is accurate or accurate enough and has been what I used but I noticed files all had cutouts for these round hygrometers…
Well from my 6 pack 1 is within a margin of error to even be useful.
I get they aren’t expensive but seems like a waste of money for this bad.
I’ve tried the old spring one’s too, and the spring quality determines the accuracy, but again, not over time. Turns out the Inkbirds are equally as accurate as the Protmex showed, all the TermoPro’s were junk, and after a brief chat with ThermoPro customer service they refunded my entire purchased which was over 6 months ago, so that was nice. I think my body has been conditioned by bad Hygrometers to misjudge waht 40% rh should feel like, but the inkbirds were a good find, am gonna keep the protmex to do spotchecks on the inkbirds every nowa and again