Quote from bighog:
Volume is always "ZERO" volume until price triggers orders.
On the ES, when the DOM shows 1200 x 400 (Ask / Bid), please share with the class how Price moves without 1. Volume eating away at the price level, or 2. Pulled orders (Volume) being removed from the queue (or a combination of the two). Price cannot move forward unless or until Volume at the given Bid / Ask Pair removes orders resting at those levels. Volume isn't triggered by Price change. volume causes price change.
It's really that simple.
- Spydertrader


You can see this happen watching MarketDelta's Bid/Ask footprints.