Sounds like this is the type of thermometer you stick into the meat and leave in while it's cooking. If that's the case, you can only calibrate it with another thermometer you know to be accurate.
Consider buying a digital instant read thermometer that has a range the exceeds the boiling and freezing-points of water. It's a much more versatile thermometer on its own and can be used to measure the accuracy of your current thermometer.
"If you want to make an apple pie from scratch, you must first create the universe." -Carl Sagan