Exchange 2007 "Messages Sent/sec" value increments rather than showing current flow

Exchange 2007 "Messages Sent/sec" value increments rather than showing current flow

Hi all,
My instinct says this counter should show current mail flow levels/second but the counter appears to be showing a constantly incrementing total of all messages sent since the Exchange services were last restarted.  Is this an error or an expected behaviour?  I note that this value behaves the same way in the free Exchange health monitor as well as Op Manager
 
 
Thanks
Paul D
 

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