Plotting board

A plotting board was a mechanical device used by the U.S. Coast Artillery to track the observed course of a target (typically a moving ship), project its future position, and derive the uncorrected data on azimuth (or direction) and range needed to direct the fire of the guns of a battery to hit that target. Plotting boards of this sort were first employed by the Coast Artillery around 1905, and were the primary means of calculating firing data until WW2.