The slie rule (often nicknamed a "slipstick") was developed by William Oughtred and others (see history, below); it is a mechanical analog computer, consisting of at least two finely divided scales (rules), most often a fixed outer pair and a movable inner one, with a sliding window called the cursor. The slide rule is used primarily for multiplication and division, and also for "scientific" functions such as roots, logarithms and trigonometry, but does not generally perform addition or subtraction. The Binary Slide Rule manufactured by Gilson in 1931 performed an addition and subtraction function limited to fractions.