Thats what I initially did, but if you get inconsistant readings yet again, or if you are just unlucky to get one just as inaccurate, giving the same inaccurate reading and you take it to be accurate since 2 are reading the same..? Sorry I am a little paranoid about things like these and husbandry stuff. But why spend more on numerous possibly inaccurate devices that don't give you a sure answer when you can use the salt test (its pretty simple DIY) and be able to calibrate or just know how much to add/reduce from a reading?

I doubt that there is such a great difference in the humidity in your enclosure from the warm side to the cool end, its really difficult to get that kind of humidity gradient. But in any case, do you happen to know roughly what the humidity of the air in your area is? Since both have such great differences you could take a pretty good guess if you did. Like the way I found out my first digital hygrometer was wayyy off - I took it out and it read 40%, air in my area never dips below 55 though. So pretty obvious there. I tried exhaling onto it for half a minute and it read 50%, confirmed it was totally off. Just to ask, are you using a lamp for heating?