Polhemus Celestial Computer and Plotting Board

This unusual device was designed for use in aircraft. It gives arithmetic and vector solutions for speeds of 90 to 2000 knots, with consideration of errors due to acceleration, and a dead reckoning capability of a plotting board. Although some of its functions are mismatched for navigators on slow speed vehicles, others such as Polaris Q correction, motion of the body, motion of the observer and coriolis correction will be useful and interesting for the user.

The back side of the computer is designed to accept its 7 detachable chart templates. These provide a lambert conformal display on which to plot course and position information for latitudes up to 70° north or south. One of the templates is of a small area plotting board design. The templates rotate on a base grid which allows for the solution of any trigonomical vector problem.

The computer comes with a 52 page illustrated instruction manual covering its operation in conjunction with standard navigational techniques. Computer, manual and the templates are contained in a 3 pocket, heavy duty plastic carrying case.

These computers were surplussed by the military in the mid 70s when we acquired them. We last sold them in 1990. Although the computer and templates are very high (milspec) quality, the cases and manuals are not in the best condition. Some cases have cracks in them, and their closing snaps may have some rust. The staples in the manuals have also attained some rust over the years. Diameter is 8.5 inches. SW 2.0 lbs

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