If you got any numbers like this, you are on the right track.In the case of a service time that is appreciable, e.g. 2 seconds, a slightly more complex analysis is required (see <a href="http://cs.nyu.edu/courses/fall09/G22.2434-001/capplanrulethumb.html,">http://cs.nyu.edu/courses/fall09/G22.2434-001/capplanrulethumb.html,</a> but the idea is simple.