[SalesForce] Tracking Field History on Opportunity Product

I suggest following one of these two approaches:-

If the values in product are to be considered only at time, opportunity is created i.e. if values changes, then it has no impact to past opportunities

1. Create fields (viz. X and Y) on opportunity product to persist these values (present in product)
2. Create workflow to populate these fields (X and Y) on opportunityproduct creation, which will pull these field values from related products
3. Create a third field Z on Opportunity line item, which calculates (Z = X * Y)
4. Create a rollup summary field on Opportunity to rollup value of field Z on related opportunityproducts

If the values in product are to be considered at all times i.e. if values changes, then it has needs recalculation for past opportunities

1. Create fields (viz. X and Y) on opportunity product to persist these values (present in product)
2. Create trigger on Prodict to detect change field values, to populate these fields (X and Y) on all related opportunityproduct records with modified products
3. Create a third field Z on Opportunity line item, which calculates (Z = X * Y)
4. Create a rollup summary field on Opportunity to rollup value of field Z on related opportunityproducts