After you enable introscope.agent.jmx.ratecounter.enable=true in the IntroscopeAgent.profile you see a new set metrics :
<jmx_metric>_rate (per interval) metric.
How does the java agent calculate the *_rate counter metrics?
Let say the value of first data point is X on time t1 and the value of second data is Y is on time t2 , the value of CompletedRequests_rate (per interval) in the above example will be Y-X on time t2.
X=106,844 and t1 = 10:26:15PM
Y=106,871 and t2= 10:26:30PM
CompletedRequests_rate (per interval) => Y-X = 27