Special Propeller Protractor
A 1928 NASA technical note, a plain report issued for engineers and aeronautical researchers, presenting a special propeller protractor and its layout method. The first plate shows drafted layouts of centre lines and stations on a propeller blade, while the second shows photographs of the protractor's graduated dial, pointer arm and fittings. A designer could take from them the precise, schematic look of early mechanical measuring instruments, with fine radial graduations, tick marks and labelled numbered callouts.
