Ok people i appreciate this might me a bit long winded but ANY help would be
appreciated.

i have a table called "Customer_Details" and i have 3 other tables calls
"tariff 1", "tariff 2" and "tariff 3".

The Customer_Details table has a form with the same name and on that form
there is a field called "tariff" which is a drop down box with tariff 1,2 and
3 in it.

Also on the Customer_Details form is a Balance field which is linked to the
same on the table.

finally there is a table called "data_live" this is continually added to on
a day to day basis, the fields are : Acc No, Cost, Prod ID.

on the tariff tables each product has a product id

Basically want i want to do is on the customer form select a tariff, then
when the data is entered into data_live the correct tariff is apllied to the
product (via product id) then i think i am write in saying that i will be
able to create a query that sums up all the prices for that customer (via Acc
No) and displays the result in the Balance field.

any help at all would be great

many thanks