Abstract: A secondary datum scheme is used for identifying the location of the core-produced internal geometry of hollow investment cast metal parts that are made using a free-floating core design for implementing complex internal structural features. A set of datum pads are cast on a removable portion of the core print out to provide the secondary reference system. This secondary reference system precisely establishes the location of the core-produced internal geometry of the part exclusive of any fixed external primary datum structure/system so that, for example, precision machining and gauging may be performed upon such internal features during subsequent fabrication steps.