Delta is the term we use to describe the net difference between the buying and selling entering the market.  It is calculated by subtracting the volume transacted at the bid price from the volume transacted at the ask price.  By definition, MarketDelta considers trades that occur at the ask price to be trades initiated by aggressive buyers.  Trades that occur at the bid price are considered to be initiated by aggressive sellers. Thus, a positive delta would reflect more aggressive buying as the result of motivated buyers lifting the ask.  A negative delta would reflect more aggressive selling as the result of motivated sellers hitting the bid.

Calculation:     Ask Traded Volume – Bid Traded Volume = Delta

Example: If the bid price in the market is 1445.25 and the ask price is 1445.50 and 25 contracts/shares trade at 1445.50, then the delta would be counted as +25. If a second trade occurs with the same bid and ask price in the market, but this time the trade occurs at 1445.25 for 10 contracts/shares, then the delta for that trade would be -10 and the total delta would now be +15.