Phonograph records are generally described by their diameter in inches (12-inch, 10-inch, 7-inch) (although they were designed in millimeters), the rotational speed in revolutions per minute (rpm) at which they are played (, , , 45, 78), and their time capacity, determined by their diameter and speed (LP playing, 12-inch disc,  rpm; SP 10-inch disc, 78 rpm, or 7-inch disc, 45 rpm; EP [extended play, 12-inch disc or 7-inch disc, or 45 rpm); their reproductive quality, or level of fidelity (high-fidelity, orthophonic, full-range, etc.); and the number of audio channels (mono, stereo, quad, etc.).