Product review (2 stars): Poor Accuracy
I have purchased 3 of these and all of them very in temperature. I use them in aquariums for sensitive freshwater fish. Accuracy is poor, usually running 3.4 to 5.0F above temperature at 78F submersed. I have a calibrated test instrument to check them but a quick way to check them at home is the following. Get a large glass or insulated sippy cup and fill it with Crushed ice. It needs to be crushed. Stick a pencil in the middle and fill it with water. Wait a few minutes and remove the pencil. You will be left with a nice hole to stick your probe. Insert the probe. Wait  2 minutes then move it up and down a bit. If the gauge is accurate it should read exactly 32F. If not at least you know "approximately" how much to add or subtract at any given temperature. It could be further off or better let say at 72F room temperature.