Engine performance and the determination of absolute ceiling
A 1924 NASA technical report on aircraft engine performance and how absolute ceiling is calculated, written for aeronautical engineers and aviation researchers. Its two pictures are plain graph plots with a fine square grid, one curve rising steeply then flattening against altitude in feet on the vertical axis. A designer could draw on them for minimalist data-plot motifs, graph-paper textures, or the clean, unornamented look of early engineering documentation.
