Abstract: A plurality of portions of an open-end spinning machine are dynamically coupled to a plurality of magnetic discs for generating a plurality of pulse sequences indicative of the operating speed of the spinning unit portions, i.e., sliver supply speed, yarn withdrawal speed, etc. The so-generated sequences of pulses are routed through a cyclically operated multi-tap switch into a main and an auxiliary binary counter. The output states of the various counters are out-pulsed to a memory and to a data transmission line after being filled during each switching interval of the multi-tap switch, such interval normally being set by a clock pulse generator. In order to generate ratios of the measured quantities, i.e., the machine draft, the clock pulse generator is overridden and the auxiliary counter initially measures a quantity (i.e., the sliver input rate) indicative of the divisor of the ratio.