Four days ago Goal Seek and Auto-build went live — tools that add to a system. As of this morning the other half of the set is live too, and it works in the opposite direction. Trim tells you which of your rules to take away. Frontier tells you whether the numbers in those rules are the right ones.
Between them they answer the two questions that follow every promising back-test: am I carrying rules that are costing me money? and why did I pick that number?
Trim — the rules worth removing
Systems grow rules the way lofts grow boxes. You add one to lift the strike rate, another to cut a bad going band, a third because it looked right at the time — and the sample quietly shrinks under you until every statistic rests on eighty runs.
Trim is the mirror image of Goal Seek. Instead of suggesting rules to add, it takes each rule you already have, re-runs the back-test with that rule removed, and tells you what it is really contributing. Every rule comes back with one of four verdicts:
Drop — the runners this rule excludes actually carry an edge, so removing it improves your target. Loosen — it barely moves the needle either way, so it is a volume lever you can relax for more bets. Keep — genuinely load-bearing; removing it weakens the system. Redundant — it excludes nothing your other rules do not already exclude, so it is doing no work at all.
Click Remove on anything marked Drop, re-run, and you will often find the leaner system makes more — from more bets, with a bigger sample behind every figure. That is the part people find counter-intuitive: taking rules out is frequently the improvement. Each suggestion carries the same one-click robustness check against the last 12 months you get everywhere else in the builder.
Frontier — pick the number from the curve
Most systems have one number doing the heavy lifting. Odds under 8. A rating rank of 3. A field of at most 12. Ask most people why that number and the honest answer is that it looked about right.
Frontier settles it. Pick the rule and it re-runs your entire back-test once for every value on a ladder — under 4, under 5, under 6, all the way out — and charts the trade-off at every step: how many bets you get, against what they return. It also plots the rule-off point, so you can see the same system with that rule removed entirely.
The shape of that curve is the story. A smooth slope means the edge fades gently and your exact threshold is a matter of preference — take the volume. A sudden cliff means one value is carrying the whole result, which is a classic over-fitting warning and worth a robustness check before you trust it. Found the sweet spot? Click Use and the rule updates to that value.
Built to keep working
The discipline is the same one that runs through the whole builder. Trim will tell you a rule you are fond of is doing nothing. Frontier will show you that the number you have been using for two years sits on a cliff. Neither is comfortable reading, and both are considerably more useful than a tool that agrees with you.
The walkthrough for Trim is above; watch Frontier sweep a threshold here, or start with the full System Builder guide. If you missed part one, Goal Seek and Auto-build are covered here.
The System Builder is included with Proform Premium.
