SLIDE RULE. An instrument composed of sliding scales, and used to perform certain arithmetical calculations. The annexed figure shows the Nestler rule. In using this scale for multiplication the figure 1 on the slide is made to coincide with one of the two factors on the scale, the product then being found opposite the other factor as read on the slide. In division it is necessary merely to place the divisor read on the slide above the dividend read on the rule, and the quotient will be found on the rule below 1 on the slide. For involution the numbers on the upper scale of the rule are the squares of the numbers on the lower scale, and the cubes can be found by inverting the slide. The inverse of this gives the square and cube roots. On the reverse of the slide is a scale of sines and tangents, and a scale by the use of which logarithms may be found.