Line Mover — hold-margin book (soccer)

The trader's-hand view of a multi-way book. The Margin — multi-way (Shin) page shows the two global operations — strip a whole priced market to fair, or apply a margin to a whole fair distribution. This page shows the local one the ops desk actually does all day: money lands on one outcome, you move that one price, and the rest of the book has to follow so the house margin stays exactly where it was.

Pick a market, and the seed odds load with their margin already measured. Then push any single outcome up or down — one decimal-odds ladder tick with the −/+ steppers, or type a price straight into the field. The outcome you touch is the driver: it lands exactly where you put it. Every other outcome is a follower: with the margin locked, the followers re-price so the overround Q = Σ 1/dᵢ — and therefore the margin m = Q − 1 — never moves.

Market1X2 (Home / Draw / Away)Half Time / Full TimeCorrect ScoreExact Total GoalsWinning Margin

The flagship 3-way. Home favourite, ~4.8% overround. Push any outcome up or down with the −/+ steppers (one ladder tick) or type a price directly. With margin locked the outcome you touch lands exactly where you put it and the rest of the book re-prices to hold the overround Q = Σ 1/dᵢ constant, so the margin m = Q − 1 never moves. Unlock it to see the margin drift when only one price changes.

Margin (locked)4.81%

Overround Q1.0481

Outcomes3

Target margin %

Lock margin (rebalance on nudge)

#	Outcome	Decimal odds	Δ price	Implied q	Fair p	Shade q−p
1	Home (1)		—	0.4762	0.4587	+0.0175
2	Draw (X)		—	0.2778	0.2626	+0.0152
3	Away (2)		—	0.2941	0.2787	+0.0154
	Σ	held		1.0481	1.0000	+0.0481

Fair p is the margin-free distribution recovered from the current book by the Shin strip (the same solver as Margin — multi-way); Shade q−p is the margin loaded onto each outcome, which Shin weights toward the favourites. The driver's decimal is exactly the price you set; followers are shown to three places, since holding Q exactly generally lands them between ladder ticks — production snaps them to the published grid, which reintroduces a sub-tick margin wobble the exact readout here deliberately ignores.

What "keep the margin the same" means

The book's margin is the overround Q = Σ 1/dᵢ minus one: the amount the implied probabilities sum above a fair 100%. Shorten one price and its implied probability qₖ = 1/dₖ rises; unless something else gives, Q rises with it and the margin creeps up. To hold the margin you have to take that same amount of implied probability back out of the other outcomes — lengthen them until Q returns to its locked value.

The tool keeps the exact implied-probability vector q as the source of truth and shows 1/qᵢ rounded to a sellable decimal on top. That is deliberate: the margin readout is computed from the exact q, so it stays pinned to the last digit even though the displayed prices round. The two rebalance bases differ only in how the followers share the load:

• Proportional scales every follower's q by one common factor. It preserves the priced ratios of the untouched book — the shape of the rest of the market is unchanged, only its overall weight shifts. This is the default and the closest match to how a trader nudges a line by hand.
• Equal shifts each follower's q by the same additive amount, so every other outcome absorbs an equal slice of the move regardless of how long or short it already is.

Both pin the driver exactly and both hold Q exactly; they only disagree on the followers. Unlock Lock margin to drop the invariant entirely: now a nudge moves only that one price and the margin readout drifts — the contrast that makes the locked behaviour legible.

Reading the table

Fair p strips the current book to its margin-free distribution with the same Shin solver the Margin — multi-way page runs, and Shade q−p is the slice of margin sitting on each outcome — Shin loads more of it onto the favourites, which is why the shade column is not flat. As you move a line these update live, so you can watch a manual price move redistribute not just the prices but the underlying fair view and the margin weighting.

Target margin re-prices the whole book to a new overround in one step (every outcome scaled together) — the "tighten the book to 6%" or "loosen it to 4%" move — after which nudges hold that new target.

Scope

The catalog is genuine partitions: outcomes that are mutually exclusive and exhaustive, so the fair probabilities sum to one (1X2, Half Time / Full Time, Correct Score, Exact Total Goals, Winning Margin). Overlapping books — Double Chance, Draw No Bet — are intentionally excluded: their outcomes are linear combinations of the same base results, so nudging a displayed price in isolation would imply an incoherent underlying (home, draw, away) distribution rather than a clean line move. The followers are shown to three decimal places because holding Q exactly generally lands them between ladder ticks; production snaps them back to the published grid, which is where the perfectly-held margin picks up its real-world sub-tick wobble.