Multiple Hosts on one graph

[linuxchris]

Hi,
I am using Cacti 0.8.4 and would like to know how I create a graph that contains data from several hosts. An example would be several sendmail servers that all are currently graphed for outgoing and incoming mail messages. How could I create a graph that totals up all of the outgoing messages and incoming messages? This would make it much easier to get a total number of messages being send and recieved.
Thanks