It means that the ask was hit 850 times and the bid was hit 422.
There is no way to know how many of those was right hip pocket to left hip pocket.
That's why I like the money flow indicator, it seems to give a better picture of the way the stock is moving because hip pocket transactions don't usually have any positive or negative money flow unless they are using them to walk a stock up or down, but even then they tend to balance out.
News 
Market Data 
Discover 
