As historical background to 1959 Doppler radar navigation systems, an animated film considers the use of Ptolemy and Mercator's maps, the magnetic compass, and John Hadley's 1731 sextant. Clarence Rice, aviation products manager of the Bendix Radio Division in Baltimore, MD, points out that aviation navigation depends on knowing the ground speed and the path of the aircraft over the earth. He uses a chart to demonstrate the effects of winds on plane direction and the efforts to compensate: a homing device, which did not account for wind drift and also picked up static interference; the radio range system, which used four beams to overcome the drift problem but still received static; and the manual direction finder, which became the standard aid in the 1930s. A film describes how, in 1939, Bendix developed the automatic direction finder (ADF) with omnirange, which also eliminated static. Over the ocean, LORAN, or long range navigation, devices were used. Another animated film shows how Christian Doppler, in 1842, described the Doppler effect based on sound waves and how that principle has been applied to radar's radio waves. The film explains the "plus" Doppler effect for direct measurement of forward speeds and the "minus" for measurement of drift angle. Pitch and roll are also corrected by the radar beams since beam compensation is based on the magnitude of the Doppler shift. A plane's Doppler radar components include a transmitter, antennae, receiver, frequency tracker, and cockpit indicator. Mr. Rice explains how pilots divide their flights into shorter legs, placing the information into the navigational computer. He notes that Doppler radar will not become obsolete with faster aircraft speeds and that it does not require a land-based facility.