Plotting Board Mark 7 MIL-B-5046B MiG-21 Embossed on its face is

Embossed on its face is "AC USARMY" (see close-up photo)

Here is a WWII-era Pilots' Information File published by the US Army Air Force with revisions through April 1945

used for the Twin Compass System

published in October 1939

the angle can be obtained

Plotting Board Mark 7 MIL-B-5046B MiG-21 Embossed on its face isThis is an authentic US Navy pilot's Chart Plotting Knee Board Mark 7 (MIL B 5046B), likely 1950's to Vietnam War era. Likely designed for a jet aircraft (note fuel is measured in lbs), this 9. 5 x 7 x 1 inch device included the flight computer on the face with a rotating card for determining the critical factors impacting the planned flight. By depressing a button in the lower right corner, the top flips open to reveal a map compartment, clips for