Validation depends on cell value

[SteveT]

if cell a1 = b1/2 user should choose if 1st half of order or 2nd half.
The answer will post as a result in c1. In other words if a1 = 25 and b1 =
50 the user should choose if c1 equals 1 or 26 (1st or 2nd part of total
units in cell B1)

any help greatly appreciated.

Steven

 

[Jason Morin]

In the "Formula" box under Data > Validation > Custom:

=OR($C$1=1,$C$1=$A$1+1)

HTH
Jason
Atlanta, GA

 

[SteveT]

I should clarify couple of things
a1 is input cell and the validation will only effect the NON visible cell
c1.
The validation should only inact if cell A1 is one half of value in cell B1.

I am thinking that cell validation is the way to get user to choose whether
c1 should start with 1 or b1/2+1 as don't know of other way to get user to
choose
one or other. If another excel tool or function would serve purpose better
I'm open to suggestion.
Thx, Steven