I have a situation in which I have several columns of numerical data,
each grouping containing 80 sets of numbers. The user enters numbers
into column A and column B, and they will be totalled in column C.
(Other coding prevents displaying the total until both numbers are
entered and checks for other validity).

This happens from C1 - C30, then from C41-C70, with a total of 8
groups per column.
The next 8 groups are in columns D-F - the user enters a number into
D, and another number into E and the total appears in F.

If data validation worked on calculated columns, I would have it
made. But...

If the totals within any group are duplicates of a previous total
within that group, then I want to have a message pop up warning the
user that this might be an error (it might be correct, though, so I
want just a warning). The warning would read something like "double-
check your entry to be sure that it is correct." The message could
always be the same.

I am self-taught in Excel, mostly from reading this group. However I
have almost no knowledge of Worksheet Events and Class Modules,
although I have been reading this group for help and also looking at
Mr. Pearson's site and trying to grasp it all.

From what I have read, I think I can do this with a series of
worksheet events such that the events would be triggered when data is
added into columns A or B to check the newly calculated total in
column C against other totals in column C for that range grouping, and
then pop up a message to alert the person entering the data to double-
check their entry.

One slight problem - once the message has been triggered for a
specific entry, I would not want to trigger it again for that same
entry just because another set of data was entered into the grouping
triggering the event Of course, if a new set of data triggered the
message because the new set created a duplicate in the totals column,
then I would want the message again.

Is this possible? Am I on the right track? Here is my example,
assuming entries to be done in order by the user, and the third column
to be calculated.

EG - GROUP 1

A B C Event

2 3 5 None
3 3 6 None
1 4 5 Trigger a message to double check the entry
4 4 8 None (I would not want to re-trigger the message)
4 2 6 Trigger the message now...
etc


EG - ANOTHER GROUP

D E F event

4 4 8 None (even though it duplicates an entry in group 1 -
I don't care)
3 3 6 None
2 3 5 None
3 5 8 Trigger the message since it duplicates an entry in
this group.
5 5 10 None
1 4 5 Trigger the message