Select cells I26:I28. Under Data, Validation, choose Custom
Formula is:
=COUNTA(I$26:I$28)=1

similarly, your other range will use a validation formula of:
=COUNTA(I$36:I$38)=1
--
Best Regards,

Luke M
*Remember to click "yes" if this post helped you!*


"ran58" wrote:

In a worksheet, the user may assess intermediate target achievement in
cells I26:I27:I28 and final target achievement in cells I36:I37:I38 as
follows
- target on track respectively target
achievement exceeded
- target achievement unclear respectively target achievement
almost complete
- target not reachable respectively target not
achieved
For each cell the user may declare his judgement by entering an "x".
How can I manage that, similar to conditional formatting, he or she is
only allowed to enter one "x" in the respective range? Thus, if I
enter an "x" in cell I26, the other cells I27:I28 must remain blank
(and same procedure for the range I36:I38). Many thanks for any
suggestions