Multiple choice list narrowed by selected company?

No problem, that is called a Conditional Drop down.

edit the field properties for related contact, and set it to be conditional on the section of related business

Conditional values The values in this field depend on a selection in another field


The only show Contacts matching Related Business.


.

Okay, thanks for your help! I finally got that part working. The next step up is more complicated. I need to have a purchase order with multiple line items attached. Then I need to be able to create a shipment that has attached parts from a selection of the line items from the purchase order. Been working on it for two days and cant wrap my head around the relationship logic. I know it is going to be a conditional drop-down but its difficult because I need the line items to only have one complimenting attached part. 


Puchase Order --------> Line items
  |                                          |
  |                                          |
  |                                          |
 V                                         |
Shipment                              |
  |                                          |
  |                                          | 
  |                                          | 
 V                                         |
Attached Parts  <---------------

I am struggling with Quickbase. I am used to writing direct functions with PHP or ASP.net and this is proving difficult to learn. :$

The typical initial setup would be

One PO has many Line items  typical;ly written like PO < Line Items
One Item Master SKU has Many Line Items Item master SKU < Line Items

ie the wide part of the < points to the many side of the relationship.


 so that is the typical many to many join that for the line items which will have the qty and the price.

Then it sounds like One PO has many Shipments
One Shipment has many Attached Part Assignments
One PO Line Item has many Attached Part Assignments.

SO Attached part Assignments are akin to the "line items" on the shipments.

The drop down list for the Attached Part Assignments will be conditional on first selecting a [Related Purchase Order]. That [Related Purchase Order] will be a lookup from the Shipments table.