Tito 4 These type of thermometers are good for backup awareness of a thermostat failure and a general idea of aquarium temps. They're usually pretty accurate at least around room temp ranges. Also, since they stick onto the outside, you don't have to worry about your more energetic fish knocking them down because there's a tiny bit of algae around them (my pleco knocks everything around in my aquarium). They're also useful for brewing if you do any of that.This one has a clear sticker on the numbered side as well, so don't forget to take that off as well. You pretty much can only stick these on once. If you try to pull it off, it could get warped and become inaccurate, so make sure you line it up well before removing the sticker backing.