Currently, PMI allows for comparing metric values of only the same metric element. For example it is possible to compare interface A bytes in, on system A with interface A bytes in, on system B. It is not possible to compare interface A bytes in, on system A with interface B bytes in on system B. The metrics provide similar numbers, but there is no mechanism to compare them currently in PMI on OBM.
It is possible to graph the same metric for interface A and interface B on system A. It should then be possible to have a graph of two different interfaces on two different systems.