 "Concerto for prepared piano" (1950–51) used a system of charts of durations, dynamics, melodies, etc., from which Cage would choose using simple geometric patterns.The last movement of the concerto was a step towards using chance procedures, which Cage adopted soon afterwards.A chart system was also used (along with nested proportions) for the large piano work "Music of Changes" (1951), only here material would be selected from the charts by using the "I Ching".