Slide rule workshop C

Nathan's third mystery slide rule.

“EngPen” tubular slide rule

Data:

  • Article by Nathan Zeldes in JOS.
  • Made by the EngPen company in Chicago; no other information on its origins.
  • We know really nothing about this pencil slide rule, except for US patent 883,800 granted to William S. Harlow, of Swampscott, Massachusetts, which describes an instrument that is not completely identical to this one.
    William S. Harlow got two later, unrelated, patents for electrical switches. Andries de Man
  • Evidently intended to be placed around a pencil (as in the Harlow patent), but too wide for current pencils.

Questions:

  1. Is there a relation between the EngPen Company in Chicago and William Harlow?
  2. More info?