Money Flow (MF) is the product of price and volume. Positive/negative MF
occur when today's price is higher/lower than yesterday's price. The MFI is
calculated by dividing positive MF by negative MF for the past n
periods. It is then scaled between 0 and 100.
MFI is usually calculated using the typical price, but if a univariate series
(e.g. Close, Weighted Close, Median Price, etc.) is provided, it will be used
instead.