Delta: measuring the tug of war

Delta is the difference between aggressive buy volume and aggressive sell volume over a period: delta = volume at the ask − volume at the bid. A positive delta means buyers in a hurry dominated; a negative delta means sellers in a hurry did. It is the numerical measure of the tug of war between the two sides, and the most widely used order flow tool.

Delta can be computed at every scale: for a candle, for each price within a candle, for a whole session. It is always read with price next to it: on its own, it means almost nothing.