Scanning electron micrograph (SEM) of the surface of a long-playing, stereo record with a scratch across the grooves. The grooves are cut into a flat disc of polyvinyl chloride (PVC). The nature of the groove varies with the intensity of the music: the straighter the groove the quieter the music, the more wavy the groove (as here) the louder the music. The stylus travels through the groove & picks up the music modulation from the sloping sides; it is transmitted to the cartridge where a piezoelectric crystal or an electromagnet converts the vibration into an electrical signal. Magnification: x17 at 35mm size, x120 at 8x10-inch size. Reference: MICROCOSMOS, figure 9.17, page 182.