This package holds the diagnostic messages which provide the
     standardized interface for the diagnostic and runtime monitoring
     systems in ROS. These messages are currently used by
     the diagnostics
     Stack, which provides libraries for simple ways to set and access
     the messages, as well as automated ways to process the diagnostic
     data.
      
     These messages are used for long term logging and will not be
     changed unless there is a very important reason.
     
diagnostic_msgs is a package to hold the diagnostic messages
These messages are used by the runtime diagnostics system.
See the wiki at http://pr.willowgarage.com/wiki/diagnostic_msgs for a summary of the messages.
And the diagnostic system is documented at http://pr.willowgarage.com/wiki/Diagnostics