Identifies which unit and what type of data is being reported.
A value of 0 means that this MIB information comes from the top-level system
view (eg, manifold module or system bypass cabinet reporting total system
output). Standalone units also use a value of 0, since they are the 'full
system' view.
A value of 1 or higher indicates the number of the module in the system
which is reporting only its own data in the PowerMIB objects.