One possibility: You're "clearing" the manual number by using the space
bar. That leaves a space character in the cell and the comparison with
the null string fails.

If that's the case, you can use

=IF(ISNUMBER(B9),B9,A1/B1)






In article ,
Jean9 wrote:

I've tried your suggestion and when entering the manual number it works but
when no manual number, the calculation does not work at all. What I'm I
doing wrong?

Jean9

"Gary''s Student" wrote:

Use two cells:

Say in Z100 we usually have =A1/B1, but sometimes we want a manual value
instead. In Z100 enter:

=IF(B9="",A1/B1,B9)

so if B9 is empty, the formula is used. If B9 has a value, the value is
used.