In contrast to automated machines and installations, manual assembly still lacks real-time process monitoring and possibilities for short-term control and adaptation of assembly systems. This article describes an approach for a concept of real-time control of manual assembly systems. For this purpose, KPIs that can be determined predictively are considered. These indicators enable a standardized and objective process data acquisition and a local process optimization for a higher flexibility and adaptability. In addition to the key figures developed, an approach for the automated acquisition of appropriate process data in manual assembly is described. The further usage of the KPIs and the validation within a real production environment is finally presented.