Here the sign ↔ (correspondent) is used instead of = (equal). Formally, hertz (Hz) and radian per second (rad/s) are two different names for the same SI unit, s−1. However, they are used for two different but proportional ISQ quantities: frequency and angular frequency (angular speed, magnitude of angular velocity). The conversion between a frequency f (measured in hertz) and an angular velocity ω (measured in radians per second) are:
The LP (long play), or 331⁄3rpm microgroove vinyl record, is a format for phonograph (gramophone) records, an analog sound storage medium. Introduced by Columbia Records in 1948, it was soon adopted as a new standard by the entire record industry. Apart from relatively minor refinements and the important later addition of stereophonic sound capability, it has remained the standard format for vinyl albums.
At the time the LP was introduced, nearly all phonograph records for home use were made of an abrasive (and therefore noisy) shellac compound, employed a much larger groove, and played at approximately 78 revolutions per minute (rpm), limiting the playing time of a 12-inch diameter record to less than five minutes per side. The new product was a 12- or 10-inch (30 or 25cm) fine-grooved disc made of vinyl and played with a smaller-tipped "microgroove" stylus at a speed of 331⁄3rpm. Each side of a 12-inch LP could play for more than 20 minutes. Only the microgroove standard was truly new, as both vinyl and the 331⁄3rpm speed had been used for special purposes for many years, as well as in one unsuccessful earlier attempt to introduce a long-playing record for home use.