Digital movies are still in the introduction stage of the business life cycle. Most prints are still made of physical film (several reels) that must be spliced together. Projectionists "build" movies by splicing ads, trailers, PSAs, and the film reels into one large circle of film. Projectionists also "break down" movies after their run is over, thread movies through the projector, clean projectors/the projector booth, fix any presentation problems that occur (including brain wraps, static wraps, mis-frames, sound problems, etc), and maintain humidity; especially in theaters that use ELF platter systems.