Candy thermometers clip to the side of a saucepan for gauging the temperature of candy mixtures, sugar stages, or preserves. They are designed to register temperatures between 230°F and 350°F (110°C and 180°C)-the range to which sugar syrup-based mixtures are heated in the making of candy, preserves, and various desserts. Because readings will vary with altitude, calibrate the thermometer by using it to measure the temperature of boiling water. The difference between your reading and 212°F (100°C) should be applied to the temperatures given in the recipes.