I was not sure on a descriptive Subject for this so I used If Than statement
due to if I were using Crystal Reports that is how I would do this:

I pulled this data from a Crystal report, the below are order promise dates
and order receipt dates. The first date is the Promise date the second is
the receipt date so in order to track on time shipments I would take the
first column and subtract the second however I came across several issues. 1.
is when you see a blank line that means the first row after that is a
different part number then the number above. 2. is that we may receive
several shipments of the same part with the same promise date. 3. is that you
will see on the last line that there are three rows and the last has a
different promise date which means on that order for that part number two
different promise dates were issued.

I started out with an IF statement that stated that if receipt date is
receipt date above it then subtract that receipt date from the promise date
to get days late. This worked for two row but caused issues when it got to a
blank row and a single row of dates. So I am not sure how to get past that,
then on the last group when it changes promise dates I don't know how to get
past that issue either.

Any ideas for me to try??

3/28/2008 5/9/2008

4/11/2008 5/9/2008
4/11/2008 5/16/2008

5/16/2008 5/2/2008
5/16/2008 5/9/2008
6/13/2008 5/9/2008