For example, suppose the machine repeatedly fails to pick up the wafers. An engineer will be assigned to solve the problem. He or she is not necessrily the person who originally designed the Step_LD (and the control system). Assuming no prior knowledge, he or she will first examine the design table and decide that the sequential stages from DP222543.1 to DP222543.7 should be checked, because the physical wafer pick up occurs at DP222543.7.