copying values from sheet to another
 

Hi!

The problem is this:

I need to copy values (for example how many units sold) from one sheet
to another. The tricky part is that "main sheet" has all the products
in column A and other sheets only a small part of them in column A and
additional values in column B, C, D .... How could i "compare" these A
columns and add the values to "main sheet" when there is a match.