Rolling ruler

A rolling ruler is a ruler that contains a cylinder much like a rolling pin inside, thereby enabling it to "roll" along a sheet of paper or other surface where it is being used. A rolling ruler can draw straight, parallel lines, and also has other instruments included, enabling it to do the jobs of a protractor and compass.[1][2]

A rolling parallel ruler
Antique rolling rulers

The modern rolling ruler, with protractor, pivot pin and multiple pin holes serving as fixed length compasses has been patented in the US in 1991 by Wei Wang. [3]

References
  1. Jack E. Ingels (2003). "Using Drawing Instruments". Landscaping: Principles and Practices. Cengage Learning. p. 11. ISBN 9781401834104.
  2. Jim Tolpin (2007). "drawing techniques". Measure Twice, Cut Once. Popular Woodworking Books. p. 24. ISBN 9781558708099.
  3. U.S. Patent 5,050,309
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