The way to achieve this was to make a wide rule with as many pairs of scales as were required; in particular many sliding interfaces were needed, which was solved by having not one but two slides, with scales on both sides, for a total of eight interfaces (compared to two on the Coggeshall).Engineers, meanwhile, needed to do the generic calculations of multiplication, division, and square roots; and for that purpose James Watt, the inventor of the steam engine that powered the industrial revolution, devised about 1790 a simple and convenient slide rule called the Soho (after the location of Watts workshop in Birmingham).He took this design to the Tavernier-Gravet firm the successor to Gravet-Lenoir and had them produce it as a standard item in their product line. The Mannheim slide rule was extremely effective, and became a standard configuration produced by numerous makers well into the following century.The cursor was of the Chisel type, with two fingers jutting to the left of the sliding rectangle; the thin tips of these fingers would point at the scales.As a collector interested in the evolution of technology in time, I made an effort to acquire one representative of each stage in this evolution, and have finally secured all but the very earliest (for items pre-dating the 19th century, rarity and price do conspire against the collector! This article uses photos of the items I have and one that I dont to illustrate the history of the straight logarithmic slide rule and its cursor.
The iconic slide rule, long identified with the science and engineering professions before the advent of the electronic calculator, had two sliding components that set it apart from an ordinary rule: the slide running down the center of its body, and the transparent hairline cursor (also called runner) that moved over both body and slide.To do that, youd need a cursor, a sliding member that traces a perfect perpendicular line across the rule. Who invented the Cursor (or, as it was sometimes called, Index, indicator, or Runner) is debatable.There is mention of some form of cursor devised by Isaac Newton in 1675, and another is described by Frenchman Philippe Mouzin in 1837.they used fixed scales on a wooden rule that allowed distances to be measured and added using a pair of dividers.This "Gunter's Rule" was the original device introduced by Edmund Gunter in 1620, which remained in use for some two centuries.