I have two metal (similar to a Brewmometer) thermometers and one floating thermometer. All three have significantly different temps. I brewed yesterday and this was very frustrating during the Mash...

Even when all three thermometers were in water, they had three different temps. This was very concerning when I was preparing the Sparge water at 170 degrees.

Any suggestions?

You won't be able to reset the floating thermometer (sealed alcohol bulb thermo, IIRC) but the two metal ones should have adjustment screws on them somewhere.

One way to adjust is for freezing (32F or 0C) by placing the thermo in a glass of water with ice in it. The BrewMometer doesn't go to freezing so if yours is like that one this may not be an option for you.

The other is to set to the boiling point (212F at sea level).

Thanks for the reply...

Will the thermometer stop and hang on 212 in boiling water or keep rising?
So when is boiling boiling? Is it when it's rolling? What should happen at 212 degrees?
ALSO...

I think the metal thermometers I have only list as low as 32. I have a $5.00 thermometer in my chest freezer which seems acurate according to the temp contol thermostat. Could I place the metal brewmometers in the freezer and adjust the screws to be the same as that one?

THANKS AGAIN FOR YOUR HELP!

Yeah, at sea level, water can't get above 212. When it does, it turns to steam. So,at a rolling boil, you should be sitting right on 212.

I use a lab grade thermometer to calibrate my brew thermometers. They're very acurate. Some are only acurate in a specific range though.

As Doc suggests, I too use a lab calibration thermometer. Mine is mercury filled glass and it stays in a protective metal case even when measuring the temperature. I will calibrate my other thermometers (bimetal dial) using the calibration one for reference AND calibrate at or around 150°F. I agree that using ice water and boiling water at sea level should give you 32° and 212°, respectively. However, some cheap thermometers don't seem to be linear and may read correctly at freezing/boiling temps but are significantly off at mash temperature ranges. After all, that's the critical range for brewers.