A. C. Fowler patented this rule Nov. 17, 1891. Very simple construction. Marked "The Combination Rule, Square & Compass Pat'd Nov. 17, 1891". No markings on back.
Patent # 463212. (Note: There are other examples with a June 10, 1891 date).
Brass that was factory nickel plated. Six and a half inches long with lots of holes.
The center row of holes is on 1/4" spacing. There are extra holes going across at the 3" point. Five more smaller holes on the left end.
Using a pin in the hole on the zero line, you can then make circles from 1/2" to 11 1/2" in 1/2" increments.
Using one of the other holes on the left ends allows to shift the rule and make circles of other sizes.
Drawing a line and then putting the long row of holes on the line, you can use the holes at the 3" point to mark two points that will be perpendicular to the line.
Using the straight edge, you can then mark a perpendicular line.
I think it's pretty clever.
Fowler 1.jpg
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Originally Posted by Jim Koepke
