I dont know if any of he other guys really covered this but another flaw in getting a rating based on the finishing is the pace at which a race is run, a slow pace obvioulsy isnt going to favour the back markers and a fast pace is not going to suit a front runner. Also another thing that cant be factored in is whether a horse is blocked for a run coming down the straight or if the track has any bias in it or for that matter the length of the straight and how tight the last bend is, for example the difference between Doomben & Eagle Farm. I think there is to many factors to take into account before you could before you could confidently come up with a mathematical rating to represent a horses finish.