+=head1 EXAMPLE 3
+
+C<rrdtool create proxy.rrd --step 300
+DS:TotalRequests:DERIVE:1800:0:U
+DS:AccumDuration:DERIVE:1800:0:U
+DS:AvgReqDuration:COMPUTE:AccumDuration,TotalRequests,0,EQ,1,TotalRequests,IF,/
+RRA:AVERAGE:0.5:1:2016>
+
+This example is monitoring the average request duration during each 300 sec
+interval for requests processed by a web proxy during the interval.
+In this case, the proxy exposes two counters, the number of requests
+processed since boot and the total cumulative duration of all processed
+requests. Clearly these counters both have some rollover point, but using the
+DERIVE data source also handles the reset that occurs when the web proxy is
+stopped and restarted.
+
+In the B<RRD>, the first data source stores the requests per second rate
+during the interval. The second data source stores the total duration of all
+requests processed during the interval divided by 300. The COMPUTE data source
+divides each PDP of the AccumDuration by the corresponding PDP of
+TotalRequests and stores the average request duration. The remainder of the
+RPN expression handles the divide by zero case.
+