Why all the focus on convoluted formulas? Its easy to fool yourself that you are doing something worthwhile and useful just because its based on some (apparently clever) mathematical calculation.

The easiest way to determine class and the class runners in the field is to glance through their form classify them based on the class of races each horse has won, been competitive in or failed. It takes about 20 seconds per horse to give you a feel...probably the same time or even less than it does to perform some of the calculations suggested.

The end result is a much more reliable indicator of what level each horse has won or been competitive in. That is something practical that can be used in form analysis rather than a number with a decimal point that doesn't really tell you much at all.