Barometric scale
Tags: FAA Pilot's Handbook
Barometric scale. A scale on the dial of an altimeter to which the pilot sets the barometric pressure level from which the altitude shown by the pointers is measured.
Barometric scale. A scale on the dial of an altimeter to which the pilot sets the barometric pressure level from which the altitude shown by the pointers is measured.
The adjustable barometric scale is necessary because of the effects that atmospheric conditions have on static pressure. At sea level, air exerts 14.7 pounds per square inch. However, as altitude increases, pressure also decreases.
In order to compute the density altitude at a particular location, it is necessary to know the pressure altitude. To determine the latter, set the barometric scale of the altimeter to 29.92" Hg and read the altitude.
  
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