It's a good idea to check the accuracy of your candy thermometer before each use. Place the thermometer in a saucepan of boiling water for a few minutes, then read the temperature. If the thermometer reads above 212°F., add the same number of degrees to the temperature specified in the recipe and cook to that temperature. If the temperature reads below 212°F., subtract that number of degrees from the recipe temperature. Don't forget to add or subtract that same number of degrees from the cooling temperature if the recipe lists one.