Thanks for the reply! I like the addition of an index and that may be the key. There are too many items and transactions to consider inserting a row manually.
What if we reverse the sort order so index:1 is the most recent date with the known QOH. Would this eliminate the need for a new row? I still don't know how that would look....
QOH = IF index = 1, then use QOH from Item Table,
Calculate( QOH - Qty Change, Index-1)
?? Does that make sense?