The knocking characteristics of fuels in relation to maximum permissible performance of aircraft engines
This is a 1939 NASA technical report on engine knock in aviation fuels, produced by the National Advisory Committee for Aeronautics for aircraft engine researchers and engineers. Its pictures are plain line graphs with gridded axes, plotting specific fuel consumption and a knock-related ratio against fuel-air ratio and inlet air temperature, with labelled curves and data markers. A designer could take from them only the clean, utilitarian chart conventions: thin gridlines, legend boxes, and sparse, labelled data series.
