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As it applies to drag racing, Corrected altitude is the adjustment in feet above sea level based on weather conditions. The importance in this is the closer to sea level you get, the more dense the air is. The more air an engine can cram in a cylinder, the more power the engine makes.
Most index and bracket racers depend on weather stations correcting the altitude for weather conditions, so that the racer can predict his ET. These calculations are also important for tuning the car. Such as selection of carburetor jets.
Density altitude is the altitude in the International Standard Atmosphere at which the air density would be equal to the actual air density at the place of observation, or, in other words, the height when measured in terms of the density of the air rather than the distance from the ground. "Density Altitude" is the pressure altitude adjusted for non-standard temperature.
Both an increase in temperature and, to a much lesser degree, humidity will cause an increase in density altitude. Thus, in hot and humid conditions, the density altitude at a particular location may be significantly higher than the true altitude.
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