1st item: Eckel Dial-O-Matic Engineer's or Engineer's Log Log slide rule, manufactured by Lithocalculator Company, Arcadia, California, circa 1955. Comprised of two celluloid-coated aluminum disks, one on top of the other, with a clear plastic cursor, the end piece held together with a metal screw. Includes an instruction manual for the Layman's model with additional insert for the Engineer's model, and a brown plastic case. Slide rule: 7 1/2" dia (includes cursor). 2nd item: RotaRule Model 510 50" pocket size circular slide rule, manufactured by Boykin Products Company, Ruxton, Maryland, circa 1963. Comprised of double-sided white plastic with a clear plastic cursor with a white plastic end piece held together with metal screws. Includes brown leather case, instruction manual, a Rota Rule parts lists, and a miniature screwdriver, with original box. Slide rule: 6" dia (includes cursor). Box: 8 3/4" H x 6 1/4" W x 1 1/4" D.

CONDITION: Slide rules in overall very good condition with expected surface wear. Boxes, cases, instruction manuals with minor tears, dampstaining, general wear to be expected from age and manner of use.