Set of four ivory triangular rules, stamped with various conversions, arranged by William Ellis Metford, and made by Pastorelli and Company, London, 1850-1869

This is the rule for someone who needed, or loved to have, a great deal of numerical information. Each of the 12 available rectangular surfaces and half of the triangular ones are crammed with figures and scales. There are plain rules in various divisions of the inch, scaling rules for map-reading, trigonometric lines and trigonometric equations, the areas and circumferences of circles and spheres and equations for finding areas, expansion coefficients and specific gravities of various metals and water, conversion scales for English to French and Rhineland feet, and to metric, information for ranging, gravity, and equations of motion.