The Money Flow Index (MFI) is a momentum indicator that measures the strength of money flowing in and out of a security. It is related to the Relative Strength Index(RSI) but whereas the RSI incorporates only prices, the MFI also accounts for volume. Instead of using "up closes" versus "down closes," money flow compares the current interval's average price to the previous interval's average price and then weighs the average price by volume to calculate money flow. The ratio of the summed positive and negative money flows is then normalized to a scale of 0 to 100.
You choose how many intervals to go back for the previous price, the look back period (This application uses default length of 14 periods).