build smaller versions for the front of buses and trains, and by 1977 revenue from these had already surpassed that from other lines of business. The displays often required minor maintenance to free up "stuck" discs. Alternative technologies Flip-disc systems are still widespread but are not often found in new installations. Their place has been filled by LED-based products, which use a small amount of power constantly rather than each time the message changes, but are easily visible in light and darkness and, having no moving parts, require little maintenance. Some producers offer combined displays that use flip-dot and LED technologies together (every dot-disc has its own LED) and thereby they combine their advantages. For example, the Czech company BUSE from Blansko supplies self-patented DOT-LED displays (only DOT and only LED as well) in Central and East Europe. This combined technology was used for outside displays of most of new buses and trams. Application See also History of display technology Vane display, a display using a similar mechanism but configured as a 7-segment display Digital micromirror device References External links Display technology Ferranti Computer-related introductions in 1961