Mean Average Deviation (MAD) is an exponential average of errors between forecasted sales and actual sales, regardless of whether the errors are positive or negative. It is a measure of the normal variation of the data for that SKU. Statistically, four times MAD is the outer band where only 1% of the points are expected to fall outside this range. So, new sales data in excess of this level is highly suspicious and most likely does not represent normal sales history.