A PCB (printed circuit board) is a component that contains other parts mounted on a substrate. Only the IEC TR 62380 and RDF 2000 models support an additional failure rate calculation specifically for PCBs that takes place in addition to the failure rate calculations for the individual parts in the PCB. Neither of these models can be mixed with other models because the methodology that they employ is significantly different than the methodology employed by other models. Consequently, the IEC TR 62380 or RDF 2000 model can be selected only for the top-most assembly in the System Tree Items table, and this selection cannot be overridden for lower-level assemblies or parts.