A unique running value used as index into the table.
When not 0, this index is interpreted as the slot number
(within the chassis) containing the entity that is using
licenses. If corresponding entPhysicalIndex (RFC 2737) exists
for this slot, celPhysicallyProgEntIndex contains its value.
When referring to a physical entity for which a slot
is non meaningful, but entPhysicalIndex exists, this index
has a value 0 and the object celPhysicallyProgEntIndex
contains the corresponding value of entPhysicalIndex.