Essential activities for the achievement of trouble-free software development are monitoring a software product and management of a software project. Monitoring changes that have major impact, however, is usually a very hard to complete because every engineer usually could not know entire source code in detail. In this paper, we propose our metric for source code updates based on component rank. Software components and their use-relation alter as development goes. The component rank also changes as a response to the changes of use-relation among components. We use the degree representing change of component rank as a metric of impact for a source code update in a development. We applied the metric to open source projects, and demonstrated that the metric is useful to know refactoring activities or important updates. We also discuss how the metric can contribute for process management.