My thermometers vary greatly. Using a digital multi-meter and a temperature probe, I filled a test tube with DI water, put a rubber stopper with a 1/8” hole through the center of it on the top of the test tube and fed my temperature probe down into the DI water. I then sealed the hole in the rubber stopper and submerged the test tube ¾ into the electrolyte. This works like a charm! It is very consistent when cross checked with other thermometers. For the rest of my tanks, I use a variety of hand held digital cooking thermometers and IR units.
Here is a glass encased, water filled temperature probe housing that I made for the temperature probe on my multi-meter.
Here is the multi-meter temperature probe in action...Wonderfull!
