Test in ice and boiling water, and in the same hole (or as close as you can get) in meat. My older Thermopen went bad after 8 years of use. Twenty five bucks service charge and it came back like new. I have a second one I'm gonna have serviced (7 years of use/storage) before I give it as a gift. These puppies are seriously handy when they are working. Just don't heave it into the trash bin. Or if you do, heave it into my trash bin, please!