My column headings a
A = Description
B = 1st Half
C = 2nd half
D = total year

in cells B10 and C10 the user is to enter the "calendarization" %, i.e., the
% of total sales that occur in the first and second half of the year. Because
it is redundant, I have NOT aggregated the total in cell D10.

I want to display a visual warning if the % entered in B10 and C10 exceed
100%. For now, I have planted an "error" message in the unused cell D10 which
is remains as long as the total does not exceed 100% but which appears,
through Conditional Formatting, in bold red lettering if the total exceeds
100%.

Is there any other way to display such an error message, through Validation
or VBA?