Lugan, when you sell 100 shares, those shares do not go directly to the buyer . Those shares go to the market maker. The maket maker will then turn around sell those shares to the buyer and pocket couple pennies difference.
So to accurately find out how many shares actually traded hands (from sellers to buyers), you take the total volume divided by 2.
A long time ago the volume as reported as both a buy and a sell. A decade or so again they changed the rules for SOME of that. Now I believe the number generally represents about 60% of the added buys and sells at the end of the day.
As with everything else in this country of ours, transparency is praised, but not believed in.
Only thing I'm sure of is that Wave's buying comes in ebb tides and ebb flows/