I'm setting up a spreadsheet that will summarize data based on multiple
(though simple) conditions.

Specifically, the base data will include several columns - year, month,
product, salesperson - and then a sales amount. I'm trying to set up a
series of formulae that will sum the sales amount, only if desired conditions
are met in the first four columns ( i.e. exact year, exact month, exact
product and exact salesperson).

The only way I've found to do this successfully is using an ARRAY FORMULA.
This concerns me because the workbook will contain hundreds of these formulae
(covering every possible permutation) and I'd like it to update easily.
ARRAY FORMULAE seem difficult to update, copy, paste and edit.

Is it easy to update a large number of array formulae automatically, or is
there another way to sum data based on multiple conditions, as described
above?

MANY, MANY, MANY THANKS!!!

Marika :)