Hey, In my opinion. The most useful measurement of productivity is a relationship between planned work, interruptions, and re-work. If an engineer spends 1 hour on doing productive, creative work and 10 minutes on rework (testing and corrective actions included), you can safely assume that is a highly productive engineer. If the team is spending less than 60% of their time on the work they are planned to be doing vs interruptions, support to previous projects, etc. you know that the team is not productive and the amount of time expected on rework will be increased. That how we do in our company, check vilmate.com