A medical thermometer has a bulb-shaped base containing a chemical which will expand when heated - typically Mercury - enabling the temperature to be measured by observation of the volume of the mercury. Attached to the base is a tube, marked with temperature values, which indicate the temperature of the mercury when it reaches them. When the bulb is inserted into the human mouth, a doctor or nurse can determine the patient's body temperature. Many thermometers are present in the Stargate Command infirmary along with a variety of other pieces of medical equipment.
In the year 2000, Teal'c and Colonel Jack O'Neill claimed Earth was stuck in a time loop which only they were aware of. Skeptical, Major General George S. Hammond ordered them to undergo a medical examination which involved their temperature being measured with a thermometer. The results showed no abnormalities. (SG1: "Window of Opportunity")