This investigation provides an empirical scaling of software engineering practices derived from the software process maturity model developed by the Software Engineering Institute of Carnegie Mellon University (Humphrey et al. 1989). An analysis of data collected in an extended software maintenance study has shown that the responses to Humphrey's key software practice items fit the Rasch psychometric model providing an alternative framework in which to understand the software development practices. The Rasch model analysis describes the likelihood of a practice deployment for any level of evolution and provides precise and meaningful measures.