film using a single, unattended projector. Two essential technologies were needed to enable this: the long-play device, a.k.a. platter, i.e. a turntable 4–6 feet in diameter or (in the case of Sword Systems and Sabre Systems by EPRAD) an extremely large film reel 3–5 feet in diameter either of which enabled the reels of a feature presentation to be joined together into a single roll, in some cases up to 30,000 feet (approx. six hours at 24fps) in length; and the xenon arc lamp, which can burn continuously and unattended for as long as is needed (most carbon arc lamphouses will run for a maximum of 40–50 minutes before the carbon rod needs replacing, and require regular adjustment by the projectionist during that time). Automation systems were also introduced, which could be programmed in advance of each screening to perform functions such as operating auditorium lighting, adjusting volume levels and changing audio formats. Some would argue that these technologies reduced the skill level or downgraded the showmanship element of the projectionist's job (for example, by eliminating the need for changeovers and nitrate handling precautions). Others would argue that more advanced skills were needed in other areas. With the introduction of widescreen in the early 1950s, projectionists had to cope with the additional lenses, aperture plates and masking systems needed for different aspect ratios for the first time. Multiple channel audio systems using magnetic sound and 70mm film prints were also introduced in the 1950s, and these required specialist projection skills to handle. Like nitrate film prints, xenon arc bulbs require special safety precautions: if handled incorrectly they can explode, causing serious injury to the projectionist. Staffing levels in projection booths decreased rapidly during this period. In the classical "movie palace", the labour-intensive nature of changeovers, carbon arc lamps, and nitrate handling required large workforces of projectionists, with up to six or seven working in a single booth and a rigid management hierarchy within the profession being common. In contrast, the multiplexes of the 1980s and '90s were designed in such a way that a single projectionist can operate simultaneous screenings in 10-20 auditoria, and it is unusual for these venues to have a total projectionist workforce of more than three or four. Final film period (early 1980s–present) The job description of the projectionist began to vary considerably according to the type and location of theatre he or she worked in.