Before you trust your drum smoker temp, make sure your thermometer is accurate.
Bring water to a boil and place the probe in the water without touching the pot. It should read 212°F. You can also test it in ice water, where it should read 32°F.
If your thermometer is off and has a calibration nut, adjust it until it reads correctly. If it can’t be adjusted, make note of how far off it is.
Also remember: lid temp and grate temp are not always the same on a drum smoker.
A quick test now can save you from a bad cook later.