The 180 degree rule is a filming technique that keeps the camera on one side of an imaginary line between two subjects in a scene. Crossing this line, or breaking the 180 degree rule, can cause confusion for viewers as the spatial relationship between characters appears to change. Basic rules require characters to maintain the same left and right relationship. Examples show how the 180 degree rule is used in car chases and two-actor scenes. Match on action is a continuity editing technique where shots are edited together to make an action, like opening a door, appear fluid and continuous to the viewer.