Plain and simple but accurate and easy to read. Its hard to beat the Aqua One Internal thermometer for value. Comes complete with sucker so you can attach it in your aquarium where it will be easy to see and read.
An easy to and extremely accurate that also has a decent thermometer built in. A clear view green segment aids determination of the correct values. The hydrometer is weighted to make sure it always floats at the correct angle for testing.