This document defines consistent methodologies for computation of in-process defects per million opportunities (DPMO) metrics for any evaluation stage in the assembly process. It is intended for use in measuring in-process assembly steps rather than end product determination. Calculation of completed item DPMO is addressed in IPC-7912. A guide to defect categorization is provided that can serve as a base for summarizing and reporting in-process defects when used with J-STD-001 and IPC-A-610. It can also be used to develop process step estimated yield - the expected percentage of assemblies with no defects for a particular process step or combined process steps, based on historical defect rates.