The idea for the Celestial Altitude Differential computer was conceived within the Aeronautical Charts Section of Technical Development Service and the design was accomplished by that Section. The experimental model of the instrument was constructed by the Civil Aeronautics Administration Experimental Station at Indianapolis, Indiana. The purpose of this instrument is to compute the change in altitude of a celestial body for a short interval of time, such change being due both to the rotation of the earth and to movement of an observer over the surface of the earth.n In celestial navigation, altitude observations upon two celestial bodies determine a fix, or known position. In almost any method of computing this position it is an advantage to have the observations simultaneous and in several methods it is imperative. However, in air navigation it is impractical to make the observations simultaneously, since this would necessitate two observers and two sextants. The Celestial Altitude Differential Computer enables the observer to compute a correction to the firstaltitude observed, thereby reducing it to a condition of simultaneity with the second observation and thus accomplishing the same result as would obtain if both observations had been taken at the same time.
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