A thermometer is used to measure temperature, with thermo meaning heat and meter meaning to measure. Thermometers are used to determine if food is safe to eat, fully cooked, or in the danger zone by measuring its internal temperature. There are different types of food thermometers including digital, dial, and disposable temperature indicators. Temperature is measured on the Celsius and Fahrenheit scales, with Fahrenheit being most common in the US. Food temperatures should be at or below 41°F in the refrigerator and 0°F in the freezer. Ground meats should be cooked to 155°F, poultry to 165°F, and hot foods should be held at 135°F.