I have a 200 x 100 matrix.
Down the side in column A I have clients and they are Tier 1, 2 or 3.
Across the top in row 1 I have products, and they are rated A, B, or C.

Then in the 20000 squares there is a value (corresponding to their sales
with us)

How can I get the sum of all "A1s". ie, for all clients that are Tier1, what
are their sales in the "A" products?

Thanks in advance
Daniel