EverTune is a simple concept that keeps a string in tune until it wants to be changed. It is a very exciting development in stringed instrument technology. It is a passive, all mechanical system based on trigonometry and some rudimentary physics.
Hence it is a new technology that is actually old school, its main component being a spring set in a clever position.
The benefits of this old school, all mechanical solution are that it is very rugged and reliable with only one moving part, and with all critical parts being made from high quality steel. It is also relatively reasonable in price, as opposed to servo-based (robotic) systems, and extremely effective.
It is distinct from servo-based (robotic) tuner systems: they automatically tune strings for the player, the player tunes the strings with EverTune, EverTune only keeps the strings in the exact tune set by the player.
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