New thermometer working correctly?

[katiekelsey]

New thermometer shows water is a few degrees warmer than old thermometer showed. How can I tell if new one is correct?

 

[Mebbid]

Get a glass full of ice and add water. Wait a few minutes and dip both thermometers in the middle making sure not to touch the sides or bottom of the glass. The one that says 32 is correct.

 

[tnfinfan]

Are they different kinds of thermometer? I've found glass more reliable than adhesive and equivalent to digital (although digital gives a reading that is more precise).

 

[katiekelsey]

The thermometer I had to throw out was the kind that was weighted at the bottom. (The bottom came off and I thought mercury got into my tank, but it didn't. But I threw it out anyway)
The new thermometer hangs inside the tank.
It isn't the digital type. I haven't had any luck with those. I'll try the glass with ice and water like someone suggested.