Here’s an excerpt from Brett Steenbarger‘s article at TraderFeed discussing Money Flow.
Money Flowing Out of Stocks
"Recall that dollar volume flow (aka money flow) represents the dollars flowing into or out of a particular stock or market. We look at each transaction in each stock and multiply the transacted price times the volume of that transaction. If the transaction occurred on an uptick, we add it to a cumulative total; if the transaction occurred on a downtick, we subtract it from the cumulative total. That cumulative total at the end of the day is the money that has been flowing into (if the sum is positive) or out of (if the sum is negative) the stock…."
