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