Several years ago was playing quinellas every day.... Wanted to come up with a market and could get a copy of the Daily Form Service ( the ones on the wall at the TAB, etc.) from my local club and later one of the TAB agencies.
Came up with this... there are 36 points available.. make a market to 90%....
So if a runner got 18 points, it became 18/36 *90... so it was 45 which made it a 5/4 shot... now I know this is not short enough however it was some sort of guide... The easiest way was to multiply the points by 2 and half.. so say 8 points ( multiplied by 2 and a half) gave 20% or a 4/1 shot...
It was only very rough but as I say a bit of a guide...
Unfortunately the TABs put in Tabitha, and I then wasn't able to get varying amounts on .