A producer of picture frames uses a tracking signal with limits of

±4 to decide whether a forecast should be reviewed. Given historical information for the past four weeks, compute the tracking signal and decide whether the forecast should be reviewed. The MAD for this item was computed as 2.

Weeks Actual Sales Forecast Deviation Cumulative Deviation Tracking Signal 6 3 1 10 11 2 12 13 3 13 14 4 10 14