The general setup of the evaluation of a radar tracking algorithm in a civil ATC-system has been considered from an operational point of view. Both the present and the potential future use of trackdate has been taken in account. The result is a method to evaluate trackers for ATC on the basis of live-traffic data, under the assumption that a sufficiently accurate reconstructed trajectory is available. The evaluation starts with an identification of all moments the pilot or disturbances have caused changes in the trajectory and the track continuity. The resulting parts of tracks have been classified on the basis of this kind of changes. For the several subclasses quality measures with a distinct operational interpretation are defined. Therefore we Introduce an Autocorrelation function for stochastic signals that randomly start and stop continuation. Both aircraft tracks and tracks originating from other objects or from random origin are taken in account.