In the 1920s German manufacturer Eugene Dietzgen Co. designed and produced this brilliant drawing tool, the 932S Excello, for draftsmen. Check out how it works:

Amazing, no? Although the tool is German, the Smithsonian has one of these in their collection at their National Museum of American History. This one was used at Kenyon College. Here's the little case it came in, and the description:

This 2-1/4" German silver and steel metal drawing instrument consists of a teardrop-shaped plate to which is attached a mechanism that is supposed to hold a larger serrated wheel and a smaller pattern wheel. The mechanism links the wheels to a bar that holds a pen point. When the larger wheel is rolled along the edge of a T-square or straight edge, the pen point bounces up and down to make a dotted line that formed part of an engineering drawing.

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The larger wheel (5/8" diameter) is marked with one of the trademarks for the Eugene Dietzgen Co., the superimposed letters E and D inside a circle formed by the letters C and o. The six smaller wheels (9/16" diameter) also have this trademark and are numbered from 1 to 6, representing six possible dotting patterns. All the wheels are made of brass. The instrument also has the trademark and is marked: EXCELLO. The arm holding the pen point is marked: DIETZGEN (/) GERMANY. The instrument is in a rectangular wooden bar-lock case covered with black leather and lined with green velvet. The top of the case is marked: DIETZGEN (/) "EXCELLO". The top is also marked: GERMANY.

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This dotting instrument was advertised as model 932S in the 1926 Dietzgen catalog and sold for $5.15. It was part of the Excello product line, Dietzgen's second-highest level of drawing instruments. This object was used in the physics department at Kenyon College.

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