This has to be one of the most important tools for our indicators. This is where you select the moving average period to apply to the volume. Normally, volume can be somewhat turbulent and you may see spikes here and there due to some large trades. With the volume moving average (VMA) you can smooth out those fluctuations so you can see where the general direction of the volume is going (i.e. increasing or decreasing).

Generally, when an index decreases and a volume moving average increases at the same time, you can expect a reversal in the index at the point the VMA spike peaks and begins to decrease again. The same is true for when an index is increasing.

NASDAQ, 12/17/2001 - 12/21/2001, Chart without VMA.
 

As you can see, it's difficult to recognize signals on the above chart without a VMA. Yes, if you have more then 20 years U.S. markets experience it would be enough, but it's much easier if you have a VMA:

NASDAQ, 12/17/2001 - 12/21/2001, Chart  VMA - 30 min.