I got a hygrometer with the humidor, and other than being very nice to look at, I don't think it does much of anything. I did the salt "calibration" (it has adjustment) and the needle never got higher than 40%, so I set that to 75%, and now it never moves...

I did some reading, and settled on the Western Caliber III Digital Hygrometer. The instructions say that it is calibrated from the factory, and that you were not to do the "salt" calibration. There doesn't seem to be any adjustments on it at all. I did set it in my son's room with a high end humidifier, and it read the same as the humidifier and the hygrometer across the room (son has a clock with a temp / humidity gauge on it).

I keep the analog one in the humidifier, 'cause it looks good... but I also have the digital one.

Currently, after adding the Heartfelt bead tubes (70%), the humidity is up to 63%... seems to increase about 1% a day since i added it (4 days ago).