Fill a glass with ice and add cold water
Stir the mixture and let it sit for 1 to 2 minutes
Insert the thermometer probe into the ice water without touching the glass
Wait until the reading stabilizes
Check that it reads 32°F or 0°C
Adjust the thermometer if it has a calibration nut or reset feature
If no adjustment is possible, note the difference and use it as an offset
Repeat the test in boiling water if desired
Bring water to a rolling boil
Insert the thermometer probe into the boiling water without touching the pot
Wait until the reading stabilizes
Check that it reads 212°F or 100°C at sea level
Recalibrate or replace the thermometer if readings are inaccurate
Clean and dry the thermometer after calibration