You may also check [I did not] the Array-Formula:
{=COUNT(1/FREQUENCY(IF($A$1:$A$100=C1,$B$1:$B$100),$B$1:$B$1 00))}
Micky


"Wombat" wrote:

Right!

column A contains area codes (two digit numbers, eg. 30), column B customer
numbers (eg 999999)

The lists then go down listing orders. I want to count how many different
customers have placed an order per area (not counting duplicates)

Thanks for any help