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The formula below approximates the heat index in degrees Fahrenheit, to within ±1.3 °F (0.7 °C). It is the result of a multivariate fit (temperature equal to or greater than 80 °F (27 °C) and relative humidity equal to or greater than 40%) to a model of the human body.
There are more detailed generalized compressibility factor graphs based on as many as 25 or more different pure gases, such as the Nelson-Obert graphs. Such graphs are said to have an accuracy within 1–2 percent for values greater than 0.6 and within 4–6 percent for values of 0.3–0.6.
The EU standard test conditions for an air source heat pump is at dry-bulb temperature of 20 °C (68 °F) for and 7 °C (44.6 °F) for . [9] Given sub-zero European winter temperatures, real world heating performance is significantly poorer than such standard COP figures imply.
c °C to f °F: f = c × 1.8 + 32; f °F to k K: k = f + 459.67 / 1.8 k K to f °F: f = k × 1.8 − 459.67; There is also an exact conversion between Celsius and Fahrenheit scales making use of the correspondence −40 °F ≘ −40 °C. Again, f is the numeric value in degrees Fahrenheit, and c the numeric value in degrees Celsius:
The US Occupational Safety and Health Administration recommends indoor air be maintained at 20–24.5 °C (68–76 °F) with a 20–60% relative humidity, [13] equivalent to a dew point of approximately 4.0 to 16.5 °C (39 to 62 °F) (by Simple Rule calculation below).
A percentage change is a way to express a change in a variable. It represents the relative change between the old value and the new one. [6]For example, if a house is worth $100,000 today and the year after its value goes up to $110,000, the percentage change of its value can be expressed as = = %.
After its introduction in the 1979 ASHRAE handbook, research continued on increasing the accuracy of the CLTD/CLF method. Research completed in 1984 revealed some factors which were not accounted for in the original publication of the method; these findings were a result of the ASHRAE research project 359.
Conversely, the measure is symmetric when the change decreases by an equivalent amount e.g. a halving is equal to a log 2 fold change of −1, a quartering is equal to a log 2 fold change of −2 and so on. This leads to more aesthetically pleasing plots, as exponential changes are displayed as linear and so the dynamic range is increased.