I have the following: main form "customer" from a "customer" table. subform "invoices" with fields "invoice date", "invoice amount" "customer id" etc. from a table "invoices"

whenever user clicks or goes to a record in the "invoices" sub form. I would like a "total so far" control to calculate the sum of the "invoices amount" up until the date of the current record being "clicked" or selected.

i.e. for customer microsoft with invoices: 1) may 2 09, $150 2) may 3 09, $200 3) may 4 09, $500

If user clicks on record 2), "total so far" should show $350 If user clicks on record 1), "total so far" should show $150 If user clicks on record 3), "total so far" should show $850

Currently, I am using DSum function on an event "OnCurrent" in the subform "invoices" to set the "total so far" value. Is this method slow, inefficient?

Any other simpler,cleaner,more elegant,faster, efficient method using ms access features?

I want the "invoices" subform to show ALL the invoices for this customer no matter which record is clicked.