Rather than having me explain it to you and get you more confused, Wikpedia does a much better job than I would do.
"The device's original name is E-6B, but is often abbreviated as E6B, or hyphenated in other variations for commercial purposes.
The E-6B was developed in the United States by Naval Lt. Philip Dalton in the late 1930s. The name comes from its original part number for the U.S Army Air Corps in World War II.
Philip Dalton (1903-1941) was a Cornell graduate who joined the Army as an artillery officer, but soon resigned and became a Naval Reserve pilot from 1931 until he tragically died in a plane crash with a student practicing spins. He, with the support of the Navy and the godfather of modern marine/air/space navigation, P.V.H. Weems, invented, patented and marketed a series of flight computers.
Dalton's first popular computer was his 1933 Model B, the circular slide rule with True Airspeed (TAS) and Altitude corrections pilots know so well. In 1936 he put a double-drift diagram on its reverse to create what the US Army Air Corps (USAAC) designated as the E-1, E-1A and E-1B.
A couple of years later he invented the Mark VII, again using his Model B slide rule as a focal point. It was hugely popular with both the military and the airlines. Even Amelia Earhart's navigator Fred Noonan used one on their last flight. Dalton himself felt that it was a quickie design, and wanted to create something more accurate, easier to use, and able to handle higher flight speeds.
So he came up with his now famous wind arc slide, but printed on an endless cloth belt moved inside a square box by a knob. He applied for a patent in 1936 (granted in 1937 as 2,097,116). This was for the Model C, D and G computers widely used in World War II by the British Commonwealth, the US Navy, and even copied by the Japanese and Germans. These are commonly available on collectible auction web sites.
The US Army Air Corps decided the endless belt computer cost too much to manufacture, so later in 1937 Dalton morphed it to a simple rigid, flat wind slide, with his old Model B circular slide rule included on the reverse. He called this prototype his Model H; the Army called it the E-6A.
In 1938 the Army wrote formal specifications, and had him make a few changes, which Weems called the Model J. The changes included moving the "10" mark to the top instead of the original "60". This "E-6B" was introduced to the Army in 1940, but it took Pearl Harbor for the Air Corps (by then the Army Air Forces) to put in a really large order. Over 400,000 E-6Bs were manufactured during World War II, mostly of a plastic that glows under black light. (Cockpits were illuminated this way at night.)
The base name "E-6" was fairly arbitrary, as there were no standards for stock numbering at the time. For example, other USAAC computers of that time were the C-2, D-2, D-4, E-1 and G-1, and flight pants became E-1s as well. Most likely they chose "E" because Dalton's previously combined time and wind computer had been the E-1. The "B" simply meant it was the production model. If you ever see Copyright 1933 on older models, that was for his circular slide rule only"
http://en.wikipedia.org/wiki/E6B
