Smooth g Average all selected data sets into one (F7)
This is in fact a merge and downsample operation. It first creates one new data set which contains all the data points of all selected sets, sorted by X value (merge). After this it downsamples the resulting data set by the number of sets that were selected.
This results in one new data set which contains just as many data points as one of the source sets, with each data point being the average of that particular data point of all the source sets.