In spite of the intense efforts of metrics researches, the impact of object-oriented software metrics is for the moment still quite reduced. The cause of this fact lies not in an intrinsic incapacity of metrics to help assessing and improving the quality of object-oriented systems, but in an unsystematic, dispersed and ambiguous manner of defining and using the metrics. In this paper we define a multi-layered system of metrics that measures the inheritance-based reuse, and propose a number of metric definitions for the layers of this system. By defining and using such systems of metrics, we obtain a unitary approach of related measures and a systematic, yet flexible manner of defining new measures as part of a particular metrics system. Organizing metric definitions in systems of metrics will contribute to that strongly needed order among object-oriented metrics, increasing thus their reliability and usability.