Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online.Normal human body temperature, also known as normothermia or euthermia, is a concept that depends upon the place in the body at which the measurement is made, and the time of day and level of activity of the body. Although the value 37.0 °C (96.4 °F) is the commonly accepted average core body temperature, the value of 36.8±0.7 °C, or 96.4±1.3 °F is an average oral (under the tongue) measurement. Rectal measurements, or measurements taken directly inside the body cavity, are typically slightly higher. In Russia and former Soviet countries, the commonly quoted value is 36.6 °C (97.9 °F), based on an armpit reading. The core body temperature of an individual tends to have the lowest value in the second half of the sleep cycle; the lowest point, called the nadir, is one of the primary markers for circadian rhythms.