Mannheim by Dennert & Pape
Germany, c.1896, simplex, four 12.5 cm scales, celluloid on boxwood, metal chisel cursor.
In 1851 French artillery officer Amédée Mannheim standardized a set of four scales for the most common calculation problems.
The four scales include two double length, named A & B, for squares and square roots, and two single length, C & D, for multiplication and division.
This scale set became the basis of slide rule design for the next 100 years and bears his name today.
His design and use of a cursor hastened the eventual widespread acceptance of this feature.