Product Historical Margin
This module will store in the invoice line all the historical informations to allow you to compute your margin on product. We will always work in company currency and in invoice currency (to respect the OpenERP philosophy, as it is done in accounting entries for example). You now have the possibility to open a list view of your products and having the margin computed for a given period of time.
In the product form, you also will have a computed field that show you the info based on all invoice lines historic.
You can use this module in conjonction with the product_cost_incl_bom one to have the right margin computed from BOM costing.
1) The amount of the unit price in company currency in the invoice line is converted with the currency rate of the date of the creation/modification of the invoice line (not the invoice date). This choice has been made mainly because the cost price of the product is known at the invoice creation, but we don't have it at the date of the invoice (no historical values in the cost price...) !