Yes but the point is that it's just a back of an envelope estimate. I'm amazed that it's been downvoted as it's actually a technique that's used in this way all

Yes but the point is that it's just a back of an envelope estimate. I'm amazed that it's been downvoted as it's actually a technique that's used in this way all the time, or at least was anyway. I don't know about now when everyone has a smartphone.