Model 4016, Serial #51
on Oct. 25, 1904, this rare version of a circular slide rule
was the creation of Elmer Ambrose Sperry, a prolific inventor
with over 350 patents and whose name was later associated
with Sperry-Rand. His circular calculator was first sold by
Keuffle and Esser (K&E) for $20 in their 1906 catalog.
Made to resemble a pocket watch, they did not sell, probably
due to their cost, which was about four times as much as a
10-inch wooden slide rule.
Donor: Jack W. Flinn