Read about it in the book of Buff Pelz Dormeier "Investing with Volume Analysis: Identify, Follow, and Profit from Trends".
Normalized volume (%V) is a concept that uses an average of volume to plot volume. The volume total for the current bar is divided by the average volume (over the last n bars) to form a ratio. This ratio is multiplied by 100 and plotted in the same way that traditional volume is plotted as vertical bars on the horizontal plane, which creates a normalized volume scale of 0 to 100. This allows for easy interpretation of volume’s relative movements, with 50 being typical or average volume, numbers below 50 being light volume, and numbers above 50 being heavier volume.