analog ones tend to be less accurate. i would suggest digital. there are a few places you can grab them and types. i got a 2 probed temp/ hydro off amazon for a good price believe it was a zoo med or exo terra
i had problems with the digital exo terra one and so have many others.
i now dont use one as i feel that unless you spend alot of £££ then your not going to get a true enough telling.i mist 4 x a day for 4-5 mins and my cham is fine.