This article is from the Glossary of Technical Analysis Terms.
This volume indicator addresses some of On Balance Volume's shortcomings and was developed by Marc Chaikin. Where OBV assigns all of a day's volume a positive or negative value, Volume Accumulation counts only a percentage of the volume as positive or negative, depending on where the close is in relation to the average price of the day. The only time the entire day's volume is assigned a positive value is when the close is the same as the day's high. The opposite applies for a close at the day's low.
This analysis is based on the idea that stocks bottom from "panic" selling, after which a rebound is imminent. One way of measuring this phenomenon is to observe a widening range between high and low prices each day. In general a progressively wider range, observed over a relatively short period of time, can indicate that a bottom is near. Price tops are generally reached at a more leisurely pace and can be characterized by a narrowing of the price range. This measure of the trading range takes place over a specified period in order to determine whether or not an issue is being "dumped" and is approaching a bottom. A pre-requisite to a valid bottom is an increase in the volatility line above the reference line. In a similar manner, an indication of an imminent top would be a decrease in the volatility line below the reference line. As long as volatility is rising, in all probability a stock will not approach a top. It should be noted that this study should be used in conjunction with trend following analyses and momentum oscillators for confirmation and accuracy.