Bundles and kits
Sell a kit as one line and relieve every component from stock.
An item of type Bundle is sold as one line but is made of other items.
Setting one up: create the item as a bundle, then add its components and the quantity of each.
What happens on a sale: the bundle explodes into its components and each one's stock is relieved. Without this, on-hand quantities drift the moment a kit is sold.
Availability: before selling, IntuBu shows which components are short and by how much.
Two rules: a bundle cannot contain itself, and a bundle cannot contain another bundle — flatten it instead. Nested kits make stock arithmetic ambiguous.
For manufactured goods that are built rather than assembled at the point of sale, use a Bill of Material and a Work Order instead (Inventory → Bills of material).