An Investigation of the Effectiveness of Ignition Sparks
A 1931 NASA technical report investigating how effective electrical ignition sparks are, prepared for aeronautical and engineering researchers. Its pictures are scientific: graphs of pressure against spark counts and sparking potential, plus photographs of glass discharge-tube apparatus and a laboratory bench of instruments. A designer might take from them the clean grid-plotted line charts and the dense, labelled glassware rig as examples of technical diagrams.
