In order to monitor/adjust production especially in a circular knitting machine comprising several knitting systems and several yarn feeder devices, yarn is fed to active knitting systems from several supply devices operating according to at least two different yarn feeder principles, in a non-positive manner. The individually fed amounts of yarn are continuously measured by means of scanned real rotation signals of the feeder devices. In order to obtain monitoring information and/or adjustment measures, comparisons are made with corresponding set amounts of yarn within at least one range of tolerance, the extent of which is adapted at least to yarn quality and/or yarn path parameters. At least one user interface can be configured in a display in a computerised production monitoring/adjustment device, whereby it is possible to select therein each individual yarn feeder device according to an optimum yarn transport principle for a specific knitting system, from a plurality of yarn feeder devices which are arranged on the circular knitting machine in an operative state for non-positive delivery of said yarn according to two different yarn transport principles, and to operationally allocate each individual yarn feeder device to said specific knitting system.