Electricians' operating and testing manual;
A 1910 trade handbook by Henry C. Horstmann and Victor H. Tousley, published in Chicago by F. H. Drake & Co. for working electricians learning wiring, operation, and circuit testing. Line-drawn wiring schematics show coils, switches, relays, meter dials, and terminal blocks in flat black stroke on cream paper, with letter labels — ready-made diagrammatic marks and instrument faces.
