The CumulativeMovAvg function computes the cumulative moving average of a value from the beginning of a series.
In a cumulative moving average, the data are added to the data set in an ordered data stream over time. The objective is to compute the average of all the data at each point in time when new data arrived. The cumulative moving average computes the arithmetic average of all the rows from the beginning of the series, using this formula:
CumulativeMovAvg = SUM(a1, ..., aN)/N
N is the number of rows from the beginning of the data set.