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I would also check the digital against a glass (or even a plastic) thermometer. I have yet to see a digital that wasn't off by 1 or 2 degrees from actual. Glass and even the cheap plastic seem to be spot on to a laboratory grade glass thermometer.
I prefer to use Ranco/Aqualogic temperature controllers as they are always spot on ime, but we use these at work when we need to double check: 39240 - Waterproof Stem Thermometer (usually under $20.00 online).
Thanks for the post James. I ordered one of those Stem. Going to check that against my glass and plastic thermometers and my Ranco controller (which is +2 degrees from the glass and plastic thermometers).
Now that's a really good question!
Every DIGITAL thermometer is about 2 degress higher than my Mercury glass (Tropic marin) and plastic thermometers.
Think I'l bring the new protable digital and the glass to one of the labs at work when I can get back there and ask a tech to do a calibration test on all of them.
You are never going to get an exact reading, but I always trust glass therms., stems, and Ranco/Aqualogic controllers. Anything electronic could potentially shift in calibration just as a glass therm. could vary depending on positioning within a tank or sump. Cmor has the right approach in having digitals checked for proper calibration if you are concerned.
Well James, that's my problem. The mercury says the tank is 79, the Ranco and stem say it is 81/81.8 respectively.
I'm bringing them into work next week. I spoke with a friend in QC and metrology should be able to test and calibrate them for me. Just hope we don't have an FDA inspection that day <g>.