The Volume Percentage Change is automatically calculated to project an end-of-day figure for the stock. This tells you at any time during the day how strongly trading is shaping up compared to the stock's average volume over the past 50 days.
Volume is a key way to measure supply and demand, and is often the primary indicator of a new price trend. When a stock moves up in price on unusually high volume it could indicate the stock is being accumulated by big institutional investors. When a stock moves down in price on unusually heavy volume, major selling could be occurring. You can make extrapolated guesses at a stock's end-of-day volume by viewing its intraday volume at a given time. Let's say, for example, a stock's 50-day average volume is 1 million shares. Let's also say the stock has traded 500,000 shares by the middle of the trading day. You can then extrapolate that the stock will trade a total of 1 million shares for the day. Keep in mind, however, that a stock often trades at high volume in the first and last hours of the trading day. This can lead to mistaken impressions.