In March 1986, Casio released the Sampletone (SK-1), a radical new electronic musical instrument with a built in sampling function. Until this time, the type of tone that could be produced by both acoustic and electronic instruments was limited. However, by equipping an electronic keyboard with a sampling feature that could record any kind of sound from the environment, and then use it as a sound source for playing music, musical expression suddenly took on limitless possibilities. This invention opened a new chapter in the history of musical instruments. The SK-1 became a major hit product, selling over one million units, a rare achievement for a musical instrument.