In the system metrics, the CPU usage, Heap memory usage, File descriptor usage and active thread usage of the JVMs that runs inside the cluster are shown. These values are aggregated values across all instances within the cluster. You can also view the contribution of top 3 affecting instances in the cluster by swapping "Show total statistics" toggle

Received messages graph shows the number of messages received by an UltraESB and the send message graph shows the number of messages sent by all instances within the cluster. In addition to that top most boxes show all time sent, received and error message count. Swap "Show total statistics" toggle to view statistics of top 3 instances.