[markem]

Whether the hydrometer is calibrated or not, the main thing you want to know is "what is the relative difference between the locations, if any". Most hydrometers will settle down pretty quickly, especially since you hope to be measuring numbers in more or less the same relative range. What I used to do when I had vinotemps what to move the hydrometers weekly in a cycle through all three. Remember that it isn't necessary that the hydrometer be absolutely accurate. As long as it is consistent and relatively close, you are good to go. What you care about is at what reading of your hydrometer do your sticks smoke best. You also care about when it starts to fluctuate, of course. If I set my aristocrat at 60%, then the bottom of my cabinet reads 61% and the top (where the sensor is located) reads 57% (it's a tall cabinet). That's what works for me and so as long as it is steady, I don't worry.

I prefer the remote "weather station" type systems that slave multiple readers to one display that can be outside the unit. Startup costs are a little higher, but the overall ease of use is, IMO, worth it.

Drop "wireless humidity sensor" in to the Amazon search bar and you will see quite a few options.