A thermometer is a device used to measure temperature (or temperature gradients) using a variety of different principles. There are two important components to any given thermometer: the sensor, e.g. the bulb on a mercury-in-glass thermometer, which detects a physical change in the temperature relative to the thermometer; and a means of converting that physical change into a numerical value (e.g. the visible scale on a mercury-in-glass thermometer). There are many different types of thermometers, such as those used to measure self-contained room temperature and those to measure body temperature in ailing individuals. In humans, the standard medical thermometer works by being inserted into a key area of heat to check body temperature, such as in a fever.
There are several different types of medical thermometers classified by where they are used on the body. These include oral, forehead, armpit, temporal artery, rectal, and ear thermometers. Like with any other facility operating with animals, Jurassic Park employees used thermometers to measure the temperature of sick dinosaurs. Specifically, there was at least one rectal thermometer about the size of a turkey baster in use on Isla Nublar.