Paul,

Since you are setting up the spreadsheet now, I advise you to not use
different tabs for different Salespersons, if that is what your
different tabs are. Put all of your data in one sheet, with columns
for Salesperson's ID or name, Date of Sale, Product ID, # Sold, and
Profit. Then you can easily analyze or summarize the data using a
Pivot table or basic formulas in another sheet. Spreading the same
data type across different sheets is a PITA and I would advise strongly
against it. It is also generally inadvisable, to put the same data
types (like product sales or profits) in different columns, and
particularly separated columns, when you want to summarize across them,
although it doesn't give you nearly the same grief as different tabs.

You may have to use a look up against a master list of products, which
should be on a different sheet, to get the profits per unit sale, but
that isn't all bad, since you may use the product ID column in that
master table as a data validation column for entering the Product ID in
the Sales sheet.

Let me know if you would like an example or send or post your
spreadsheet and I will send an example.

Hope this helps,

Declan O'R