Slide rule
Moving the top scale to the right by a distance of , by matching the beginning of the top scale with the label  on the bottom, aligns each number , at position  on the top scale, with the number at position  on the bottom scale. Because , this position on the bottom scale gives , the product of  and . For example, to calculate 3 × 2 (represented as 3*2 on a calculator), the 1 on the top scale is moved to the 2 on the bottom scale. The answer, 6, is read off the bottom scale where 3 is on the top scale. In general, the 1 on the top is moved to a factor on the bottom, and the answer is read off the bottom where the other factor is on the top.