Thermometers are one of the most important instruments used in the laboratory. They are a relatively inexpensive means of reliably measuring temperature, provided they are properly used. It is essential that the instruments be used in the manner prescribed if true temperatures are to be ascertained. The following are some terms that should be understood and adhered to when true temperatures are to be obtained.

TOTAL IMMERSION: Thermometer is immersed into medium up to the point of reading.

PARTIAL IMMERSION: Thermometer is immersed up to immersion line or to depth inscribed on the back of the thermometer.

FULL IMMERSION: The complete thermometer is immersed in the medium, including the expansion chamber. (These instruments are read through a window or port in the bath).

IMPORTANT: Thermometers are not always used to indicate true temperatures, particularly where they are used in methods specified by many technical societies such as ASTM. It is most important to position the thermometer exactly as outlined in the method. Any deviation can cause erroneous indications.