When I open Excel and make a SUM of several cells, the SUM is displayed and
calculated correctly. If I save the file and re-open it and change any value
of one of the cells in the SULM, the result stays the same, the SUM is not
recalculated. If I create a new SUM in this Excel file, the result returns
ZERO. Calculation is set to AUTOMATIC, F9 does not change this.