Order-flow imbalance and delta

Order-flow imbalance measures the lopsidedness between aggressive buying and aggressive selling. It is the quantitative core that footprint and delta tools express.

Delta

Delta is the simplest measure: aggressive buy volume minus aggressive sell volume (ask-volume minus bid-volume) over a bar or session.

• Positive delta — aggressive buyers dominated.
• Negative delta — aggressive sellers dominated.
• Cumulative delta — the running total across bars, a line you can chart.

The most useful pattern: divergence

The signal experienced readers prize is delta vs price divergence:

• Price makes a new high, but delta does not (or cumulative delta makes a lower high) — the rally is being driven by fewer aggressive buyers than before, hinting at weakening demand or absorption by passive sellers.
• Price makes a new low while delta fails to confirm — selling pressure may be exhausting.

This is conceptually similar to indicator divergence on a normal chart, but built from actual aggressor flow rather than a derived oscillator.

Diagonal vs stacked imbalance (footprint)

Within a footprint, an imbalance is usually defined as one side's volume exceeding the other's by some ratio (e.g. 3:1) at a given level, compared diagonally (the ask at one price vs the bid at the price below, since those are the prices that would trade against each other). Several stacked imbalances in a row mark an aggressive, one-sided move.

Honest caveats

• Delta depends on correct aggressor classification — a centralized-data feature. FX "delta" from a broker is approximate.
• Divergence is context, not a trigger. Delta can diverge for a long time in a strong trend. Use it to question a move, then require price confirmation — never short strength on negative delta alone.