The process of master scheduling inventory strategies other than MTS product is sometimes referred to as two-level master scheduling. This term comes from the fact that the MPS items configured in the planning system are not the customer-ready finished goods SKUs in ATO or MTO environments. Instead, the MPS items in these manufacturing environments are planned at least one level down from the level zero finished goods level. The sublevel items (often subassemblies or fabricated SKUs) are scheduled by the MPS to be ready in anticipation of receipt of the customer purchase order. Once the purchase order is received, components for the specific customer-required configuration are assembled and shipped to the customer. The final schedule to make this happen is sometimes referred to as the top-level MPS or sometimes as the final assembly schedule. It is the two levels, MPS and final assembly schedule, that make up what is referred to as two-level master scheduling.