In ยง, you have already experienced summing up data along an axis. In fact a range of reduction operations are possible, including sum, product (multiplying), average (summing then dividing by the number of slice labels along that axis), standard deviation, and the maximum and minimum elements.
You can select which reduction operation is applied to the rolled-up axes from the “Reduction" menu. You can also apply an individual reduction operation to a single rolled-up axis without affecting any other axes by means of the context menu attached to the reduction symbol attached to the rolled-up axis.