Sum total for all records of one field when parent is only subset ?

[MinnesotaHam]

Main table is types of vacuum tubes. Related table is ownership of various brands and shapes for each tube type, with a quantity field. Related table has summary field that calcs total of the Quantity field. This total changes as found set in main table changes.

Primary layout has records of main table, with portal for related table.

On this layout, how can I show total of Quantity field, for all records in main table, even if found set is less than all records ?

[Vaughan]

Think carefully before putting summary fields on main data entry layouts: they will create a HUGE performance hit while they get re-calculated especially as the record numbers grow. Every time it refreshes it could be a 2 to 3 second pause. Not fun.

[MinnesotaHam]

I found the answer in an old post here. Create another relationship. Use global key fields in both main and related. Then same sum calc field always finds all records regardless of found set in main table.

Concern about update speed noted and appreciated.

DB currently has 309 records in main and <600 in related.

Main will never exceed 500 and related never exceed 2000. Even this will take years.