ok I figured out how to dynamically search a date using this:
Any ideas on how to take sub summary calculations and put them and a realted field on a record in a related table?
It sounds like you need a realtionship between "that table" and transactions that matches by both StockID and date or a date range. With such a relationship you can get total purchased and total sold using either Sum functions (defined in "that table") or summary fields (defined in transactions).
The relationship match will control what records are totaled with both of these methods.