What causes Excel to lose it addition and subtraction abilities example * =sum(b19+b20). The spreadsheet was working fine until one day when I opened it to add information to the sheet, it would not automaticlly change any of the areas I had set up to add or subtract. I now have to double click the area and press enter inorder for the sheet to get the correct numbers. Any help is greatly appreciated. I use this spread sheet to track Vacation and sick leave time.