This is a problem with other APM tools, too... someone inevitably wants to know in one number how the system is responding, and the best you can do naively is t

This is a problem with other APM tools, too... someone inevitably wants to know in one number how the system is responding, and the best you can do naively is to average all of them. Defining critical transactions, and measuring them against their SLAs is really the only valid way of summarizing total application performance (x% of traffic is meeting SLA, y% is 1 stddev above, z% 2 stddev, etc).