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The need for an accurate knowledge of ground speed, drift angle and distance traveled from an initial fix has prompted the military to sponsor development of airborne Doppler navigation systems. As a result of the military development programs and the arrival of the semiconductor age, the size, weight, cost and reliability of the Doppler nagivation systems has made it attractive to commercial carriers for navigation over long distant water routes where ground-based radio navigational aids are not available. Most of the major commercial carriers have operated Doppler systems on an experimental basis and many have adapted a Doppler system operationally to their long distance navigation problems. Some users of Doppler find that the measurement of ground speed and drift angle is sufficient to meet their navigational requirements. Other users find it advantageous to couple Doppler derived measurements of ground speed and drift angle with heading and hand set course data to a navigational computer. The output information of such a computer is the integral of ground speed resolved into along course and cross distances traveled. The initial along course distance to the next way point and the magnetic course angle is normally set into the computer. When the computer indicates zero along course and zero cross-course miles, the aircraft has arrived at the way point, within the accuracy of the system. Most computers are mechanized so as to automatically transfer stages when the along course dial of the active stage reads zero.