How long is the groove on one side of a long-play (33 1/3 rpm) phonograph record?
It seems like it would be variable depending on the number of songs on each side: The normal commercial disc is engraved with two sound bearing concentric spiral grooves, one on each side of the disc, running from the outside edge towards the centre. Since the late 1910s, both sides of the record have been used to carry the grooves There is an area about 6 mm (0.25″) wide at the outer edge of the disk, called the lead-in where the groove is widely spaced and silent. This section allows the stylus to be dropped at the start of the record groove, without damaging the recorded section of the groove. Between each track on the recorded section of an LP record, there is usually a short gap of around 1 mm (0.04″) where the groove is widely spaced. This space is clearly visible, making it easy to find a particular track. Towards the label centre, at the end of the groove, there is another wide-pitched section known as the lead-out. At the very end of this section, the groove joins itself to fo
