On the knocking of gasoline engines
A 1926 NASA technical report on knocking in gasoline engines, compiled from the NACA technical memorandum series and issued for engineers studying engine combustion. The pictures are rotated line graphs of combustion speed, pressure and efficiency plotted against mixture ratio and initial pressure, with numbered data points and labelled axes. A designer might take from them the plain engineering chart style of sparse grids, thin curves and small numeric annotations.
