Bigsworth chart board

The Bigsworth chart board (The Bigsworth Protractor, Parellels and Chart Board) was a device, developed circa 1919, to aid in the use of charts for the onboard navigation of planes. It consisted of a wooden board upon which a chart was placed. Over the chart was a pivoted double parallel linking arm that could be adjusted up and down the side of the board and at the arm's end was a protractor. Its inventor was Arthur Wellesley Bigsworth (whose name inspired Captain W. E. Johns to name his hero "Biggles").
Jefford notes that the board "was produced in substantial quantities and it remained in service well into WWII when it was still providing a portable and self-contained navigation station in aeroplanes in which adequate facilities for the observer were still lacking." (p.373)