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25 Slide Rules - the original pocket calculators

image of Slide Rules - the original pocket calculators

The slide rules on display in this case are a small selection from the collection of Peter Delehar. He is a London dealer in historical scientific instruments who has been collecting them on and off for nearly forty years.

Whether in straight, circular or cylindrical forms, the slide rule performs calculations by setting off lengths of logarithmic scales against each other. It was first devised shortly after the invention of logarithms in the early 17th century. It was ideal for problems which did not require extremely high precision, since it transforms complex calculations with pen and paper into a quick manipulation of the rule.

Reckoned purely in terms of the numbers manufactured and used, the slide rule achieved its greatest success in the 20th century. However it was rapidly and completely eclipsed by the development of hand-held electronic calculators in the 1970s. Peter Delehar’s collection focuses on the instrument’s history from its origins up to the 19th century, with just one exception from the 20th century, which is displayed here.

There are three other slide rules from his collection displayed elsewhere in the Museum as part of the SIS 25 exhibition.


Objects lent by Peter Delehar, London:

08. Circular Slide Rule on a Snuff Box, by Hoyau, Paris, 1816

11. Reversible Circular Slide Rule, English, c.1840

26. Javal's Ophthalmic Slide Rule, by A. Cretes, Paris, c. 1875

27. Triangular Slide Rule with Four Sliders, by Elliott, London, c. 1870

28. Oil Calculation Slide Rule Designed by Forrest M. Towl, New York, c. 1889

29. Master Rule and Gauging Slide Rule, by Dring & Fage, London, 19th Century

30. Anderson Celluloid Gridiron Slide Rule, by Casella & Co, London, c. 1903

31. Slide Rule in a Drawing Scale, by J. Casartelli, Manchester, c. 1870

32. Circular Slide Rule, by Joseph Lamb, London, c. 1827

33. Roubicek Circular Slide Rule for Surveying, by Neuhöfer & Sohn, Vienna, c. 1870

34. Annular Slide Rule, by Elliott Brothers, London, c. 1875

36. Box Sextant with Integral Slide Rule, by Troughton & Simms, London, c. 1870

41. 2ft Gunter Rule, owned by Thomas Annand, English, 1683

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