ICla and IClb form an astable multivibrator. The astable`s signal is fed to IC1c, also to the clock input of IC2, a 4017B decade counter. That IC`s QO through Q9 outputs become high one at a time for each successive clock pulse received at1Jin 14. Switch Sl feeds one of those outputs to the 4017B`s reset input.
Whenever the selected output becomes high, the 4017B restarts its counting cycle; that determines the number of beats per measure. The network composed of C2 and R6 sharpens the ~downbeat pulse, and the network composed of C3 and R7 sharpens the free-running pulses. By making C2 larger than C3, the downbeat receives greater emphasis.