A typical ten-inch student slide rule (Pickett N902-T simplex trig)
The slide rule, or slipstick, is a mechanical analog computer. The slide rule is used mainly for multiplication and division, and also for "scientific" functions such as roots, logarithms and trigonometry, but usually not for addition or subtraction.
There are many different styles of slide rules. They are usually linear or circular. They have a standardised set of markings or scales. These scales are used for mathematical computations. Some slide rules have been made for special use, as for aviation or finance. Those slide rules have special scales for those applications, as well as normal scales.