K&E 4180 Fraction Adder
K&E 4180 Fraction Adder is a specalized linear slide rule for adding fractions. It is circular in form.
The 4180 was first shown in the 1913 hard bound catalog. It did not appear in the 1913 soft bound catalog. It last appeared in the 1915 catalog.
Scans of a 4180 from an eBay sale in Dec. 2002: