idea
Clock arithmetic
Number the twelve notes of the octave like the hours of a clock, with C at twelve o'clock. After B comes C again, as after eleven comes twelve. Arithmetic on this circle wraps around, and it describes music well. A fifth is seven steps, and if you keep adding seven you visit all twelve notes before coming back to C. The same circle works for rhythm: place the twelve pulses of a cycle around it and mark where the drum or the bell plays.