You can change the sign within your formula. If B1 is always to be negative,
=A1-B1 instead of =A1+B1, or if A1 and B1 are both to be negative,
=-SUM(A1:B1). Obviously this approach means that each formula must be
customized.
Depending on what you need to calculate and your layout, you may find it
easier to change the signs to negative (put -1 in a cell, Edit/Copy that cell,
then select the numbers to be changed and Edit/Paste Special and select the
Values and Multiply options). Then you can change the format of the formula
cells so that the minus sign isn't displayed.
