Your kitchen thermometer isn't much good to you if it doesn't accurately show the temperature. But when was the last time you checked its accuracy?
Food52 shows us two simple ways to see if your thermometer is telling you the truth. You probably guessed it, but the tests are to insert the thermometer in a pot of boiling water (a slotted spoon is an ingenious tool for holding it in the pot without scalding your hand) and/or test in an ice bath.
The thermometer should register within two degrees of 100C for the boiling water, or 0C for the ice bath.
Food52 recommends you do this when you get a brand new thermometer and every six months or so. If it's off, you might be able to recalibrate your thermometer or at least adjust your cooking for the difference in temperature.