Symetroscope, patent callipers in wood with brass scale based on "systeme Silvy-Leligois" Mathematics

Boots Ring Plan Standard 5-inch slide rule with plastic sleeve and instructions Boots Ring Plan Standard 5-inch slide rule Mathematics 1970-1980

Slide rule for triangle-mesh-reinforced concrete slabs, celluloid, copyright 1909 by the American Steel and Wire Company Slide rule for triangle-mesh-reinforced concrete slabs Mathematics 1909-1915