Hi gunny72 and shaun,
The way mine works is a combination of days since last start and runs from a spell which is then put into a formula that provides a rating. I really don't know what the actual formula is as I didn't create it but that is basically how it works.

I hope this helps.

Cheers,

Mat.

P.S. Sorry to all who got my ratings yesterday, it was quite an off day so hopefully we bounce back on Saturday. What I do find very useful is not necessarily the Overall Rating but the horses highlighted as Improvers, Peak Fitness, Speed etc. Most of the time the winner comes from these nominated horses so that piece of information may work well with some of your own form study.