Early Cox Patented Duplex Slide Rule

Manufactured by Dennert and Pape for K&E

K&E Model # 1744 in the 1895 Catalog

William Cox signed over his 1891 patent for the duplex slide rule to K&E. The first duplex slide rules with the K&E name on them were produced by Dennert and Pape for K&E. The first mention of the duplex slide rule in K&E catalogs is in the 1895 catalog. It was introduced as model number 1744 in the 1895 catalog.

Actual Specimens:

• Specimen #1 - Marked "Wm COX PAT. OCT.6 1891". Pictures from an eBay sale.
• Specimen #2 - Marked "Wm COX PAT. OCT.6 1891". Scans and pictures of a rule from the Aaron Lerner estate.

Cover page of the Cox patent:

Page from 1895 K&E catalog introducing the 1744 Cox Duplex Slide Rule: