It is likely that at your next visit to the doctor, a medical practitioner will start by taking your temperature. This has been part of medical practice for so long that we may see it as antiquated, with little value. However, the routine nature of the ritual belies the critical importance of obtaining accurate body temperature to assess the health of a patient. In fact, subtle variations in temperature can indicate potentially harmful underlying conditions such as constriction or dilation of blood vessels, or dehydration. Even changes in mental activity, such as increased concentration while solving a mathematical equation, are accompanied by measureable changes in body temperature.