The thermometer is an instrument that measurements at a temperature either directly, by reading the temperature reading against a scale, or indirectly, by reading the temperature of a liquid. The thermometer has two major components: a temperature detector where a change in temperature occurs with a corresponding change in temperature, and a means of transforming this change into some other numerical value; such as "low" or "high." A Fahrenheit thermometer uses mercury to detect any change in temperature. A Celsius thermometer only detects a difference in temperature, not any change in any other type of measurement. The main difference between these two types of thermometers is that they do not require an external thermometer probe to detect changes in temperature.
A handheld thermometer called an Axillary Thermometer is designed for use by the consumer. The reason for this design is that it has a very fast response time, which makes it ideal for use in the consumer market. The thermometer records the exact temperature that are experienced on the skin of the user, rather than relying on a known reference that can be different from one person to another. Because of its fast response time, an Axillary Thermometer can provide a true, 30-second accurate reading.
Another type of thermometers are called Temporomandibular Disorders or TMJs. Thermometers are designed to measure temperature and pulse rate in the ear, as well as the forehead and temporo-parietal joint. An accurate diagnosis can be made by using a forehead or temporo-parietal pressure probe. This type of probe is not recommended for children under 12 years of age and for women who are pregnant or breast feeding. The reason for this is that the probe may alter the blood flow around the ear, which may result in an abnormal pressure reading.