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* Normal human body temperature is 36.8 °C ±0.7 °C, or 98.2 °F ±1.3 °F. The commonly given value 98.6 °F is simply the exact conversion of the nineteenth-century German standard of 37 °C. Since it does not list an acceptable range, it could therefore be said to have excess (invalid) precision.
An early morning temperature higher than 37.3 °C (99.1 °F) or a late afternoon temperature higher than 37.7 °C (99.9 °F) is normally considered a fever, assuming that the temperature is elevated due to a change in the hypothalamus's setpoint. [15] Lower thresholds are sometimes appropriate for elderly people. [15]
For an exact conversion between degrees Fahrenheit and Celsius, and kelvins of a specific temperature point, the following formulas can be applied. Here, f is the value in degrees Fahrenheit, c the value in degrees Celsius, and k the value in kelvins: f °F to c °C: c = f − 32 / 1.8 c °C to f °F: f = c × 1.8 + 32
Most scientists measure temperature using the Celsius scale and thermodynamic temperature using the Kelvin scale, which is the Celsius scale offset so that its null point is 0 K = −273.15 °C, or absolute zero. Many engineering fields in the US, notably high-tech and US federal specifications (civil and military), also use the Kelvin and ...
Anders Celsius's original thermometer used a reversed scale, with 100 as the freezing point and 0 as the boiling point of water.. In 1742, Swedish astronomer Anders Celsius (1701–1744) created a temperature scale that was the reverse of the scale now known as "Celsius": 0 represented the boiling point of water, while 100 represented the freezing point of water. [5]
In 1948, the Celsius scale was recalibrated by assigning the triple point temperature of water the value of 0.01 °C exactly [35] and allowing the melting point at standard atmospheric pressure to have an empirically determined value (and the actual melting point at ambient pressure to have a fluctuating value) close to 0 °C.
A sustained wet-bulb temperature of about 35 °C (95 °F) can be fatal to healthy people; at this temperature our bodies switch from shedding heat to the environment, to gaining heat from it. [10] Thus a wet bulb temperature of 35 °C (95 °F) is the threshold beyond which the body is no longer able to adequately cool itself. [11]
Conversions between units in the metric system are defined by their prefixes (for example, 1 kilogram = 1000 grams, 1 milligram = 0.001 grams) and are thus not listed in this article. Exceptions are made if the unit is commonly known by another name (for example, 1 micron = 10 −6 metre).