Digital thermocouples are the most useful all-around thermometers, as they can be used both for high-temperature sugar boiling and for chocolate and ganache. Alcohol-filled glass thermometers are reliable instruments that never run low on batteries, but separate thermometers are required for different temperature ranges. Bimetal thermometers are slower to react, and are not as accurate as thermocouple technology. Surface-reading infrared thermometers are excellent for monitoring the temperature of chocolate. The same thermometer should be used each time; small differences between individual thermometers can cause inconsistent results.