I'm sure that I do not have to tell you what a thermometer is. You probably already know on your own. A body thermometer is a machine or tool that checks body temperature. The more simple thermometers are like a long glass stick with mercury in it, and this might be the one at your house. The hotter your body temperature, the higher the mercury goes. A thermometer at the doctor's office is more advanced. This one is a machine with a probe, or the long metal stick, attached. The probe goes under your tongue, in your armpits, or in your rectum. Do they use the same probe for everyone? Well, yes. Don't say, "Gross!" just yet. The probe has a cap on it, and the cap changes every single time the patient is done taking his or her temperature. A normal body temperature is 98.6 degrees Fahrenheit or 37 degrees Celsius. The rectal temperature is the most accurate out of the three. If you measured your temperature by mouth or from your armpits, your have to add one degree to make it accurate, but you don't have to do that to the rectal temperature. Even though the rectal temperature is the most accurate, this is the least used. I don't think I have to tell you why!