Williams' Accumulation-Distribution tracks the buying pressure and selling pressure.
Williams' Accumulation-Distribution (WAD) tracks buying pressure (accumulation) and selling pressure (distribution) on a security.
The pressure is determined by where the close sits within today's true range.
Williams' AD is a running sum of positive accumulation values (buying pressure) and negative distribution values (selling pressure).
Divergence between Williams' AD and the price produces the signals. As with most indicators, WAD leads the price; or in other words, when a divergence occurs, the price usually changes accordingly. For example, if the indicator is moving up and the security's price is going down, prices will probably reverse (as shown in the example above).
Also see Volume Accumulation Oscillator, Price and Volume Trend and On-Balance Volume.