Notes: "The E6-B flight computer, called MB-4 by the military between 1953 and 1958, is well known to all pilots. Among other things, it calculates density altitude, true airspeed, time-speed-distance problems, conversions between miles, knots, and kilometers, and of course wind triangles, which one entire side of the computer is devoted to. This one was made by Felsenthal, one of the major manufacturers of flight computers. It appears to have been made for the Air Force, based on the serial number that starts with “AF”, the Air Force contract number and “U.S. Property” printed on the front, and the small stamp, ¼” square, with the eagle holding three arrows (see the last picture"