Rule 1: Horse must have been in the first four in both of its last two races.
Rule 2: Add the two form figures together along with the number of days since the horse last ran.
Rule 3: Only Select horses which score 20 or less.
Rule 4: Pick the horse with the lowest score.

&?

Glenno,

I think your off to a good start as the system has plenty of merit so far.

I think what Davez meant is you need at least one more rule for your system.
As is you could end up with an odds on favorite at $1.80 or the 100/1 shot in the race as the system stands. The system is incomplete as is.

You at least need a price rule which will cover class [up or down] to a big degree and a lot else besides. If you want to avoid a price rule you will need alternative rules to indicate if the runner is up to the job. 'Won at the track and/or distance' might help or something similar if you get my drift here.

As is, your final selection will be in form and obviously fit. But that might be a runner who is regularly running in the race's class in town [lets pretend it's a Sat. metro race] or a similarly in form and fit runner stepping up 3 classes who has never raced in the city before [your 100/1 shot] or any runner in between those two extreames.