Validation applied to formula result

[Guest]

I am using a simple formula
eg. D1=A1*C1

Without complicating the question is there any way to ensure that the
formula result in D1 is only negative and a stop message given if the result
is positive.

Thanks Glenn

 

[Dave Peterson]

Maybe use an adjacent cell with another formula:

=if(a1*c1<0,"","Stop--it's non-negative!")