In addition to displays and audio equipment, there are often a lot of other components in a well-designed presentation facility. They generally add functionality and enhance image quality. In most cases, presenters won't need to work directly with these devices, but it can't hurt to have a basic understanding of what they do: Switchers are used to select between multiple video and audio sources. Most projectors have a basic switcher built-in, but in more complex systems, external switchers are used to enable projection of larger numbers of sources. Computer Interfaces process a computer's video and audio output to achieve a higher degree of projected image quality. They also enable the connection of a local computer monitor as well as a projector. Distribution Amplifiers (DAs) are used to duplicate one signal so it may be sent to several places, such as a computer's display to multiple screens. Scalers convert video, like the signal coming out of a VCR, into a format that can be displayed at a higher resolution. They are typically used to convert signals going into a projector or plasma display.