Fill a pot or saucepan at least four inches deep with clean water.
(Note: impurities or salt can significantly affect the boiling temperature of water.)
Place the pot on the stove and turn the burner on high. (Do NOT use the microwave.)
Wait until the water comes to a strong, rolling boil that does not stop with stirring.
As soon as the water reaches boiling, put the tip of the thermometer probe a few inches into the water until the water temperature stabilizes. Be sure to keep the probe in the center of the pot and away from the bottom or sides of the pot.