Self-contained breathing apparatus pressure changes with ambient temperature. As temperature decreases, the pressure inside the cylinder decreases. The relationship between the temperature and the pressure of a gas is defined by the formula "PV" = "nRT". (See Universal gas constant.) What is particularly important to understand from the formula is that the temperature is in kelvins, not degrees Fahrenheit. Consider the freezing point of water at 32 °F (0 °C, 273.15 K) and compare it to 96 °F (35.6 °C or 308.71 K; normal human body temperature is 37 °C). While 96 is arithmetically three times 32, the difference in temperature from a
Human body temperature much higher than usual. Hormonal contraceptives both suppress the circamensal rhythm and raise the typical body temperature by about . Temperature also varies with the change of seasons during each year. This pattern is called a "circannual" rhythm. Studies of seasonal variations have produced inconsistent results. People living in different climates may have different seasonal patterns. Increased physical fitness increases the amount of daily variation in temperature. With increased age, both average body temperature and the amount of daily variability in the body temperature tend to decrease. Elderly patients may have a decreased ability to generate body heat during a