Hygrometers (Analog & Digital) and all that testing

One thing I have found with Hygrometers is they are funny little gadgets. I have 3 digitals from Cigar shops and two from Target (one small and one of the wireless ones) I have a couple older analog hygrometers as well.

I've tested all of them with salt and eventually went to a Humidpak and did that. All of them are pretty close (none exact). My wireless sensor from Oregon that I got at Target is only +1% off. My Thompson digital is also +1% off. My Little Havanna quarter size digital is -1% off and the Perfecto is a whopping +8% off.

Yet, if I leave them in open air next to eachother, by the following day, ALL the digital ones read 49%. If I put my Thompson and Oregon in the humidor, they may read anywhere from 2% to 6% difference. Yet they were exact in the humidpak test. So I have come to find that different parts of the humidor may present various percentage of Rh. This of course is in a larger 200 count humidor. In the small 25 count, they read pretty much the same, yet the Perfecto is within a couple of the accurate ones.

So with testing, I've come to realize just to find one that is close. They seem to vary so much.

What I don't get is the analog ones. I know, why have them? I have two travel humidors that have a cut out for them, so I like having it in there.

So here is my question...

My buddy has one analog hygrometer and it is right on with his digital (not calibrated though). But if his digital is 70%, his analog is too. You can watch the dial move on his!

I've had about 6 (most in the trash) that I never could get accurate. For of them would register 99-100% with damp towel over them for 30 minutes. But in the Humidpak, I get anywhere from 60% to 80%. None right on 75% that the HumidPak regulates.

So I have followed advice online about turning the little screw in back to calibrate. Here is where I get stuck. What's the secret???? I turn the little screw which moves the needle to 75% and when I let go, the needle pops right back to whatever it was reading.

I'd like to at least get one of the analogs to be accurate. But if I turn the screw to much, I can leave the needle wherever I want, However I apparently break it as the needle never moves on it's own. If I put it on 25, 50, 70 or 90% it will stay there.

So how do you get the analog calibrated? My closest to 75% is one that reads 80%, but the needle always springs back to 80 after I turn the screw.

Is it a cheap analog one? I had one that did that same thing, but I have a better one now that is not so "loose" at the back so when I turn the screw it is a much tighter twist than the previous one and the needle stays.

-W.