"Boucher" circular calculator, by Stanley, Great Turnstile, London "Boucher" circular calculator, by Stanley, (glass Mathematics 1880-1890

Circular slide rule with lockable cursor arm, plastic made by Lithocalculator Company, Calfornia, USA. Circular slide rule with lockable cursor arm Mathematics

Halden "Calculex" patent circular slide rule (5 inches diameter) in case, c. 1906 Halden "Calculex" patent circular slide rule (5 in Mathematics 1904-1907

Palmer's Computing Scale, improved by Fuller, (a circular logarithmic slide rule, with numerous gauge points); on reverse side "Fuller's Time Telegraph" Palmer's Computing Scale, improved by Fuller Mathematics 1846-1880

Circular slide rule, Fowler "Magnum", in leather case with descriptive leaflet Circular slide rule, Fowler "Magnum", in leather c Mathematics

Fowler long scale calculator, circular slide rule with carrying case and instruction booklet, 1920-40. Fowler long scale calculator, circular slide rule Mathematics 1920-1940

German circular slide-rule, type KRS 40, No.1246, 17 1/2 inches diameter, fitted in a metal case 18 1/2 x 20 inches German circular slide-rule, type KRS 40, No.1246, Mathematics

Circular slide rule, Fowler "Magnum" long-scale calculator, in fitted case with instruction booklet by Harold Fowler Circular slide rule, Fowler "Magnum" long-scale ca Mathematics

Spiral scale of chords in the form of a circular slide rule, with celluloid cursor in metal mount, cardboard 4 13/16-inch diameter with descriptive leaflet Spiral scale of chords in the form of a circular s Mathematics

Circular slide rule by Pickett, metal and plastic, in leather pouch with instruction booklet Circular slide rule by Pickett, metal and plastic, Mathematics

Circular slide rule by Fowler and Co., Manchester, model RX, double faced, serial no. 7384, with descriptive leaflet in metal case Circular slide rule by Fowler and Co., Manchester, Mathematics

Fearnley's patent Universal calculator, circular slide rule with cardboard scale in fitted mahogany case, unsigned, British,1880-1900. Used at the University Observatory, Cambridge, at Madingley Road, Cambridge, England. Fearnley's patent Universal calculator, circular s Mathematics

Circular slide rule (two cardboard discs with radial transparent plastic cursor) by General Industrial Co.1788 Montrose, Chicago 13,Illinois, also marked Slide Chart Corp., 1959, Perrygraf, Marywood, Illinois Circular slide rule (two cardboard discs with radi Mathematics 1959-1960

The "Small" Pocket Calculator, a circular slide rule patented 1918, made by G. Small, Boston, in leather pouch The "Small" Pocket Calculator, a circular slide ru Mathematics

Circular slide rule, Halden 'Calculex', in leather pouch with instruction booklet Circular slide rule Mathematics

Circular slide rule with lockable cursor arm, plastic, in envelope with instructions: " Eckel dial rule", Engineers' Model, made by Lithocalculator Company, Calfornia Circular slide rule with lockable cursor arm, plas Mathematics