This is the timestamp of the last event this SmartEvent server received from a specific Correlation Unit. A stale timestamp for one particular Correlation Unit while others show recent times pinpoints exactly which regional or segment log feed has gone quiet, rather than making the admin guess whether the whole SmartEvent pipeline or just one unit's feed is affected. For example, one Correlation Unit's last-received time being six hours stale while others updated a minute ago would isolate the problem to that one unit's connectivity or the gateways it serves.