autosum/ auto calculate each item from a random list of items

[angerion]

Hi,
I have a list of sales order, each order require specific material(and size).
in order to control the stock of each material(and size), i need a formula or VBA that can autosum/ auto calculate sales order that use same material(and size).

Please check my attachment.

If possible, the formula/ VBA can works even if the 'stock' and 'sales order' sheet is on different workbook (different computer connected by Local Area Network, because the person who control stock is not the same person who control sales order, all this time we're controlling it manually)

thanks.