// Make the number of periods configurable.
mfperiods = INPUT("MFI Periods", 14, 1, 100);

// Net money flow for this period.
mf = TYP * V;

// Aggregate the net money flow over the user-specified number of periods.
posmf = SUM(IF(TYP > TYP[-1], mf, 0), mfperiods);
negmf = SUM(IF(TYP < TYP[-1], mf, 0), mfperiods);

// Compute the money flow index for this period, taking care not to divide by zero.
mfi = IF( negmf = 0, 
          IF(posmf = 0, 50, 100),
          100 - 100 / (1 + posmf / negmf));

// Plot the money flow as a wavecrest centered at 50 with overbought and oversold levels at 80 and 20.
PLOT_WAVECREST(mfi, 50, 70, 30, 1, Color.Brown, Color.Brown); 
SUMMARY("MFI({?})  {?:F2}", mfperiods, mfi);