Hi, my first time using a discussion forum so go easy on me...

SITUATION:
I have a sheet ("weekly demand sheet") 8000 rows, 100 columns. Rows contain
various reference information i.e. unique product reference, product family,
etc plus demand data by week for 80 weeks.

The "weekly demand sheet" will continue to have new rows added to it as new
products are created and new columns as the weeks go by. The demand data for
a given week should not change once inputted.

PROBLEM:
I would like to create a sheet ("monthly demand sheet") in a seperate
workbook where each unique product reference is listed and a column summing
the weekly demand data by month displayed.

I would like the "monthly demand sheet" to be updated automatically when new
products are added to the "weekly demand sheet".

It seems straight forward but I'm not having much joy, so would greatly
appreciate any advice.