29 Mar 2019: Demo file has been updated to v2. See comments for details.
Editor’s note: Geoff Gerhard of Creative Solutions is one of those “quiet” developers who has been helpfully sharing his knowledge in online FileMaker forums for more than 20 years. I personally have benefited enormously from his expertise, and am pleased to feature his first appearance as a guest author here on FileMaker Hacks.
Demo file: BillOfMaterialsDemo-v2.zip