Nesi reveals that estimation of effort is key to managing OO development projects, then documents a few rules of thumb for doing this. One lesson he?s learned from using these rules is that estimates for a whole project are not reliable if estimates for subcomponents are simply added up. As the project size increases, so does the overhead for communication and general interaction. Nesi goes beyond effort metrics and recommends that you collect metrics throughout the project and use them for continuous revalidation of assumptions and project performance. If we accept that "what you can't measure, you can't manage," this is good advice.