Notes: "This computer, or slide rule, is designed to do a more precise version of dead reckoning navigation than the wind triangle side of an E6-B flight computer can do, or do the same job as the E6-B when you donít have access to wind information before takeoff. This one takes advantage of a technique described in a Flying magazine article by Len Morgan. Basically, if you know the barometric pressure at both your starting point and ending point, and the heading to the destination, you can derive the average wind strength and direction between the two points and calculate a heading that will get you there. This one goes a step further and describes a technique for estimating the pressure difference by observing the variation in altimeter readings while flying. This slide rule was produced by the US Navyís, Bureau of Aeronautics, Special Devices Division, in 1945. The purpose was to improve the navigational accuracy of long flights over water, when conventional navigation aids were not available"