New TA/Charting, page-6529

In it's basic form VSA or VPA looks for any anomalies between price movement (spread) and volume - I think it was you a while back that questioned an increase in price not backed up by much volume - if it wasn't such an aggressive thread I would have taken the time to answer you.

So you've touched on the basic - price movement without correlating volume is anomalous and should be examined. The finer part is looking at volume and price moves not only within the body of a bar but the wicks as well and the behaviour of the preceeding and following bars. This approach defines exactly the amount of demand and supply present at a particular time. Which are the only two things a trader or investor has to have knowledge of to make sensible decisions..

Two of the popular proponents were the late Tom Williams and presently Anna Coulling.