On improvement of air flow in wind tunnels
A 1928 NACA technical memorandum on improving airflow in wind tunnels, issued by the National Advisory Committee for Aeronautics for aeronautical engineers and researchers. Its two figures are plain graph-paper charts plotting a vertical scale in centimetres against air speed in metres per second, with a curved line falling across a grid of ruled horizontal and vertical lines. A designer could take from them a sparse, technical grid and chart layout with clean hairline rules and simple axis labels.
