For what its worth.........
Take a sum of money, money that you can afford to lose,thats your budget. Make your picks then divide what you intend betting per race in half.
Every time your a/c is bigger than your starting budget withdraw the excess.
If you do that over a long enough period you will have a good idea about how "good" you are.
Its painless & once thru the first cycle/season you can always increase the initial budget and go to bigger stakes.
However, never add to your a/c over the "period/ season".
Reduce your bets if you have to otherwise you will only be conning yourself. If you can't stay afloat then the "system" is not working.........
Bets of luck.