Power Pivot question - items on one table that are not on another, can you pivot by this?

Question

Hi, I'm new to power pivot. I am trying to import two data sources from excel files. One is a list of inventory with unique chart IDs. The second is a list of actual chartIDs billed with rate and invoice#. The purpose is to easily determine what in the inventory has NOT been billed yet.

So far I can pivot but only on what has been billed and is in both tables. I want to see the exceptions that are in one table and not the other.

I set up chart ID in both tables as the relationship.

Can you walk me through how I can do that? I appreciate it.