10-Inch Electrical Slide Rule
Frederick Post model 1456 [1925-1930]

This identical page appears in the 1925, 1927 and 1930 Fredreick Post Catalogs
In gutter: "FREDERICK POST CO.   MADE IN GERMANY." 

This rule was manufactured by Koch, Huxhold & Hanneman of Hamburg. 

Rules described as "adjustable" use the DRGM 192052 friction adjusting mechanism.