edison had previously made only phonograph cylinders but decided to add a disc format to the product line because of the increasingly dominant market share of the shellac disc records (later called 78s because of their typical rotational speed in revolutions per minute) made by competitors such as the victor talking machine company. victor and most other makers recorded and played sound by a lateral or side-to-side motion of the stylus in the record groove, while in the edison system the motion was vertical or up-and-down, known as vertical recording, as used for cylinder records. an edison disc phonograph is distinguished by the diaphragm of the reproducer being parallel to the surface of the record. the diaphragm of a reproducer used for playing lateral records is at a right angle to the surface.