In 1964 Young began what may always prove his greatest work: The Well-Tuned Piano, an improvisatory yet highly structured piano work that started at 45 minutes and has, in most recent performances, extended over six hours, containing more than 50 themes and chordal areas. Young is also legendary for his sine-tone installations, assemblages of droning overtones in complex arrays of prime numbers that now explore pitch space up to the 2304th harmonic.