A compass is a tool which can be used for drawing circles and arcs. A compass usually has two legs: one with a sharp spike for fixing its position, and the other with a pencil or pen attached. The sharp spike stabilizes one leg while the other rotates around it, drawing an arc or circle. The legs of most compasses can be locked to keep the spike and pencil at a set distance. This helps draw circles with the same radius or mark specific distances, such as when constructing an equilateral triangle.