To shorten time-to-market and improve customer satisfaction, software development companies commonly want to use metrics for assessing and improving the performance of their development projects. This paper describes a measurement concept for assessing how good an organization is at finding faults when most cost-effective, i.e. in most cases early. The paper provides results and lessons learned from applying the measurement concept widely at a large software development company. A major finding was that on average, 64 percent of all faults found would have been more cost effective to find during unit tests. An in-depth study of a few projects at a development unit also demonstrated how to use the measurement concept for identifying which parts in the fault detection process that needs to be improved to become more efficient (e.g. reduce the amount of time spent on rework).