Hello,
A1,A2,A3,A4,A5,A6,A7,A8,A9,A10 with a sum formula in A11.
I have 10 cells in a row and they may be left blank or they would have a 1
placed in one of them.
One of the 10 cells requires a number "1" to be entered for statistics.
There is conditional formatting to show one color if the total of the cells
=0.
If the total equals 1, then the conditional formatting doesn't display
If the total equals more than one, the conditional formatting will change to
another color.

My question is Is it possible to put a validation in A11 that if the
number exceeds 1 then a warning box will appear and not allow them to
continue until the offending number is corrected?

Or if the validation isn't the way to go, how can I ensure that if no
numbers are placed in A1:A10 where A11 would be 0, OR more than one 1 is
entered in A1:A10 and A11 shows a total greater than 1 to stop and not let
them go further so the error must be fixed.

Any help would be appreciated. Thank you, Bob Reynolds