Domain Engineering (DE) is an increasingly popular process for efficiently producing software. DE uses detailed knowledge of a particular application domain to define rigorously a family of software products within that domain.We describe methodology for precise quantitative measurement of DE impact on software change effort. The methodology employs measures of small software changes to determine the effect of DE.We illustrate this approach in a detailed case study of DE in a telecommunications product. In the particular case the change effort was dramatically reduced. The methodology can precisely measure cost savings in change effort and is simple and inexpensive since it relies on information automatically collected by version control systems.