Local instability of centrally loaded columns of channel section and Z-section
A 1939 NASA technical report on local buckling of centrally loaded channel and Z-section columns, published for structural engineers and aircraft designers. Its single picture is a dense engineering graph with a grid plotting a buckling coefficient k against width-to-thickness ratio, with curves labelled by flange and web ratios, plus small cross-section diagrams of the channel and Z shapes. A designer could take from it the plain line-chart and cross-section diagram style of technical reference plates, with its clean black curves on fine grid paper.
