In this paper we propose the notion of change metrics, those that measure change in a project or its entities. In particular we are interested in measuring fine-grained changes, such as those stored by version control systems (such as CVS). A framework for the classification of change metrics is provided. We discuss the idea of change metrics which are modification aware, that is metrics which evaluate the change itself and not just the change in a measurement of the system before and after the change. We then provide examples of the use of these metrics on two mature projects.