In Year2 syllabus, MAD and TS methods are mentioned. Mean Absolute Deviation (MAD) is just another name of Mean Absolute Error (MAE), they have the same formula,which is:
Where et is the error, which et = yt - ŷt, and ytis the actual demand, ŷtis the forecast demand
The MAD measures the average of the errors in a set of forecasts, if a demand forecast with MAD of 300, which means the average difference between the forecast and the actual demand was 300. Ideal MAD is zero, which means there is no error in the forecasting, the large the MAD, the forecast result will be less reliable.