i'm actually gonna go straight to the running mean absolute deviation which is a little bit more advanced version of the mean absolute deviation, and then i'm gonna show you how to calculate the running sum of forecast errors, and then i'm going to show you how to calculate what is called the tracking signal which is a way to diagnose the process that you're forecasting and look for any patterns or look for any indication that the process that you're forecasting is undergoing any significant changes.