Built-in volume script allows you to enable moving average over the volume. It is useful, but not as effective since it doesn't rate extremes which are the most interesting part about volume.
Black Corsair script adds two more measurements. One that picks highs over 100 periods and averages them. It is called High Tides. The other, Low Tides, picks lowest levels and averages them.
Anything below Low Tide is considered extremely low volume. Anything above High Tide is extremely high volume. However, these are the extremes. Volume is relatively high even when it approaches High Tide or relatively low when it approaches low tide.
Good luck!