The stick-on-the-glass types are very inaccurate. When I first bought my digital, I found that the one on the glass was 8 degrees off. I'll never go back to the stick-on types. I have a bunch of the Coralife ones like you got. They are very good. Just might want to think about getting a new battery for it, never know how long it's been in the package with the battery in it. I got one and it died in a weeks time. Got a new battery, and it's been running ever since.