from a lot of reading and some ands-on experience I am at the mind set that except for extremely low or high humidity it really does not matter that much except for the last 3 days..
don't worry yourself sick over humidity. concentrate on temperature and you should be fine..
eventually you are going to have to put your trust in a thermometer..
I have used many different kinds and I finally found one that works for me.. it is a digital combination temp/hum unit made by SPRINGFIELD ,,precise temp..
I also have a digital food therm I bought from Fleet & Farm.. It has a 5" long probe and it's reaction time is quite quick..
I also had (lost it) a therm that I bought from one of the online chicken suppliers for about $18.oo
It is about a 2" dial with a rigid 6" probe.. what I like about it is that it has a nut on the back and you can adjust it .. Once you have one therm you can trust, then adjust this one to match and you have a handy one to use to probe all of your bators with.. I sometimes have 6 to 8 bators going at a time.
hope this helps some..
.......jiminwisc..........