A counter keeps track of the number of times an event occurs. Most counters are resettable.
Spotlight uses counter data collected in consecutive refreshes to compute rates that are expressed as the number of events that occur per second. It computes these rates by dividing the number of events that occurred in the last monitoring interval by the length of that interval. (Events include activities such as static SQL statement executions, result set sorts, and database data or index page reads from disk.)