Something to keep in mind is that the electronic Hygrometers are iffy for accuracy. You can't get inexpensive electronics that are truly accurate.
The best ones are the old fashioned analog ones.
Don't get me wrong, we use the electronic ones, but I use the analog hygrometer to confirm the true humidity and in my system I can put in an offset value into the electronic unit that gets them correct (plus or minis and often 5% or more) (my humidity units in the computer room while stand alone not only allow you to, but insist you use a analog or sling hygrometer to confirm humidity and then put in the right offset).
I think they were $150 or so.