In this paper we propose a class of process metrics based on the continuous monitoring of product attributes. Two such metrics are defined for the requirements analysis process, namely stability (i.e., how smoothly the process of introducing information in a requirements document flows) and efficiency (i.e., which part of the effort of the analysts is spent in reworks). These measures can be used for the timely identification of risky trends in a requirements analysis process. The paper also gives some results from an experiment on the collection and use of the measures we introduced. Keywords: Requirements, process metrics, quantitative process evaluation.