What I get a kick out of is that it's so easy to make a calibration correction chart for ANY thermometer that is isn't even funny. My MOST accurate unit is a Pt100 RTD hooked to a PID readout that I calibrated. It is what I then use to calibrate other thermometers.
What you do is go to Google Earth, and look up your place. Round to the nearest 100 feet of elevation. Look up the boiling point at your elevation. Boil RO or DI water. Insert the thermometer, and let settle for.. oh five minutes or so. Note the reading on the thermometer if it isn't adjustable.. if it is, tweak the adjustment.
At that point you are probably close enough and good enough to know the correction at mash temperature for the device.
Then put ice into relatively pure water. Up to about 100 ppm TDS is probably good enough (I say this because you generally don't need to freeze DI water for this). Let it settle for 15 minutes. Read the the reading, that is your "cold" correction factor. If, you are, for example setting up a keezer or ferm chamber this one is the likely "close enough" reading.
You can then take the slope of those two points to figure out a better correction at any temperature but I'll leave that exercise up to the reader. On an adjustable unit you can back and forth those two setting adjustments until you get it perfect if you want, but generally the thermometers are linear enough in that range that you will find it to almost be exact anyway.
But you can take a thermometer that reads way off and still use it with the correction factor you just found assuming that it's still linear. And it will indeed be accurate to better than 1F that way.
