Abstract: In a system including clock pulse data such as a network for sequencing music or multi-media data, a man/machine interface is provided which can be driven either by the operator or by a motor and transmission system. The man/machine interface contains encoders for producing tempo clock data which can be varied by the operator. Based on the comparison of the output signals of the encoders, the motor is accelerated or decelerated to eliminate the difference between the outputs of the encoders. The man/machine interface can be operated in the slave mode in which tempo clock data generated in the network is used to control the speed of operation of the man/machine interface or in the master mode when the man/machine interface determines the timing. The man/machine interface is preferably a foot-pedal.