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National Advisory Committee for Aeronautics, Report - Tables for Calibrating Altimeters and Computing Altitudes Based on the Standard Atmosphere

This report was prepared by the Aeronautic Instruments Section of the Bureau of Standards
under research authorization formulated and recommended by the subcommittee on aero-
dynamics and approved by the National Advisory Committee for Aeronautics.

During 1925 the assumption of an isothermal atmosphere which was in general use as the
standard for the calibration of altimeters in the United States was replaced by a standard
atmosphere which assumes an altitude-temperature relation closely corresponding to the aver-
age of upper air observations at latitude 40° in this country. The same standard atmosphere had
already been adopted somewhat earlier in the United States as the aircraft performance standard.

National Advisory Committee for Aeronautics Technical Reports Nos. 147 and 218 give
necessary constants, tables, and information. However, neither of these reports includes all
of the tables required for the computation of actual altitudes nor those readily suitable for use
in calibrating altimeters, since the altitude intervals for which data are given are not sufficiently
small. The present report has been prepared specifically for these purposes.

The formulas which define the standard atmosphere are given in this report, together with
other formulas giving the corrections to be applied to the standard altitude in order to obtain
the actual altitude when the necessary observations of pressure and temperature are available.

The tables necessary for the use of this standard atmosphere in calibrating altimeters and
in computing altitudes form the principal part of this report. In Table I are given the standard
altitudes at pressure intervals of 0.1 millimeter of mercury in the range 87 to 200 millimeters
of mercury and at intervals of 0.2 millimeter of mercury in the range 200 to 790 millimeters of
mercury. In Table II standard altitudes are given at intervals of 0.01 inch of mercury in the
range 3.4 to 31.09 inches of mercury. In Table III are given the pressure in inches and milli-
meters of mercury, the temperature, the mean temperature, and the corresponding isothermal
altitude at every 500-foot interval of standard altitude in the range —l,000 to +50,000 feet.
Temperature corrections for use in computing altitudes from observed pressures and tempera-
tures are given in Table IV.