turntables called record changers could play records stacked vertically on a spindle. this arrangement encouraged the production of multiple-record sets in automatic sequence. a two-record set had side 1 and side 4 on one record, and side 2 and side 3 on the other, so the first two sides could play in a changer without the listener's intervention. then the stack was flipped over. larger boxed sets used appropriate automatic sequencing (1–8, 2–7, 3–6, 4–5) to allow continuous playback, but this created difficulties when searching for an individual track.