A study of airplane engine tests
A 1920 engineering study of airplane engine performance, compiled from test data and published by the NASA Technical Reports Server, aimed at engineers and researchers. Its pictures are plain line graphs with gridded axes, straight or curved plotted lines, and labelled altitude and pressure scales, showing how horsepower, torque, and heat distribution change with altitude and air pressure; a designer might take from them the clean, technical chart style with stepped grids and diagonal data lines.
