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.
As an old toolmaker who might have dabbled in accuracy. I just shake my head when people complain about things like this because they think absolute accuracy --an impossibility-- is the important thing, (you can’t afford anything close absolute accuracy), when it’s repeatability that matters the most. Choose the one that repeats the best, toss the rest. Then learn what the “magic number” is that makes you happy to read and need to get the results you are looking for. Learn to apply some bloody “windage”.
Remember: Rick Sanchez is a dumb-ass. And you only need to be 5% smarter than the tool you are using to be successful. So be smarter than the tool and understand the process.