Sounds roughly right. Though not all of us were full time on it at all times. We also paid that just once about two years ago. It has been part time feature and maintenance work since then.
Now run that same estimate assuming we saved 600 engineers only 1 hour per week (a very conservative number by our research and feedback). $120/hr * 1 hour saved per week * 4 weeks * 600 engineers. We paid it back in less than four months, conservatively.
