List A:
Project Code Component Code Description Quantity for Project
123 456 abcd 1

List B:
Component Code Description Quantity in Inventory
456 abcd 500


I have two lists A &B, in the above format. I am trying to create a
function that will calculate total units on hand by subtracting "qty
for project" from "quantity in inventory" by "component code", and
keep a continual total as more projects are added.

For example, after putting project 123 into production, which calls
for 1 of component 456, I want to create a column that will subtract
that 1 from 500 = 499 units on hand of component 456.

I've tried a few different vlookups/matches...but have not yet found
one that works...please help!


Many thanks in advance!