Usage of the SUM function: =SUM (calculation area) (1) If the calculation area is a continuous unit area, for example, the unit area from A3 to A 17, it is expressed as =SUM(A3:A 17)(2) If the calculation area is a discontinuous unit area, for example, it includes A3 and Kloc-0/7. For discontinuous areas, use the mouse to select the first area to be selected, and then press Ctrl to select other cells or cell areas in turn.