The presentation of single or multiple part numbers in a bill of material that describes how an assembly is put together through level codes. The finished or end item is typically coded as level 0, which denotes the highest level in a bill of material, and its immediate components are coded as level 1. If a level 1 component is a subassembly, its immediate components are coded as level 2, and so on. An indented bill of material is normally used in representing levels.