M.A.D (mean absolute deviation) and it is the average of the absolute value, or the difference between actual values and their average value, and is used for the calculation of demand variability. It is expressed by the following formula.
for example:
3, 4, 9, 8, 2, 0, 1 ( the following listed numbers are called the data set).
(we add up all the numbers, divide it by 7 since there are 7 numbers in the data set)
3 + 4 + 9 + 8 + 2 + 0 + 1 = 27 ÷ 7 = 3.85
(for the next step we need to subtract the data set with 3.85)
4 - 3.85 = 0.15
9 - 3.85 = 5.15
8 - 3.85 = 4.15
3.85 - 2 = 1.85
3.85 - 0 = 3.85
3.85 - 1 = 2.85
(for the final step we just have to add all the differences' then divide it with 7 again)
0.15 + 5.15 + 4.15 + 1.85 + 3.85 + 2.85 = 18 ÷ 7 = 2.57
so 2.57 would be our M.A.D.