In what method is the rotational speed measured in?
Phonograph records are generally described by their diameter in inches (12", 10", 7"), the rotational speed in rpm at which they are played (16 2⁄3, 33 1⁄3, 45, 78), and their time capacity resulting from a combination of those parameters (LP – long playing 33 1⁄3 rpm, SP – 78 rpm single, EP – 12-inch single or extended play, 33 or 45 rpm); their reproductive quality or level of fidelity (high-fidelity, orthophonic, full-range, etc.), and the number of audio channels provided (mono, stereo, quad, etc.).