plotter An output device for translating information from a computer into pictorial or graphical form on paper or a similar medium. There are a wide variety of plotters to match the differing requirements for size, accuracy, speed, and other attributes such as color.

One of the simplest implementations is a flatbed plotter. One or more pens are mounted on a carriage that can be moved to precise positions on a bar that spans the width of the medium, i.e. the x-axis. The bar is mounted so that it can be moved precisely on tracks that lie parallel to the lengthwise edge of the medium, i.e. the y-axis. It is thus possible to move the pen to any point that lies within the available range of x and y coordinates. The pen can either touch the surface as it moves, thus producing a line, or it can be lifted off the surface as it moves. When drawing a diagonal line the computer generally has to provide only the coordinates of the start and finish points.

Although large flatbed plotters are produced it is often preferable to use the drum plotter configuration for large drawings, or for a sequence of drawings. The drum plotter has an arrangement similar to the flatbed plotter for moving the pen across the width of the medium, but the bar is fixed parallel to the axis of a drum. The medium is wrapped around part of the drum surface and is often wound onto take-up spools on either side of the drum axis. The medium has holes punched at its edges that engage with pintles on the drum and thus maintain registration with the rotation of the drum as it translates longitudinal axis coordinates.

More recent plotters may employ inkjet technology. See inkjet printer.