"Smoothed" growth rate used to calculate implied equity risk premium

On Aswath Damodaran’s website, he publishes an annual dataset that calculates the current equity risk premium implied by current market prices. The dataset can be found here:

http://www.stern.nyu.edu/~adamodar/pc/datasets/histimpl.xls

One of the inputs to the calculation is a short-term growth forecast, based on recent changes in earnings or analyst’s forecasts. This short run growth is then averaged with a long run terminal growth rate (set at the risk free rate) to produce an overall “smoothed growth” figure. However, I don’t understand the formula that is being used to average the growth figures (column M in the spreadsheet). The variable descriptions provided on his website don’t clarify this particular calculation.

Does anyone have any ideas as to how the smoothed growth is being calculated and why it makes sense to average them in this way?