Little's Law - Verify Performance Test Results

Here is something I often use (and need to lookup) when I'm analyzing performance test reports.
Most of the time, these reports are nothing but nebulous and I have no choice but to go back to the basics.

Here's the simple procedure I use to verify the sanity of the test:
Run a step load test. Get the following data from your load testing tool (averaged) per step:
1. Transactions per second
2. Hits per second
3. Think time
4. Response time
5. Number of virtual users being simulated.
6. Throughput (bytes)

Here's where the math starts:

Using Little's Law, you then then deduce the following:
Actual Number of Users in the System = (Response time + Think time) * Transactions per second

You can also verify the page size:
Page size = Throughput / Hits per second

You can tell if there is something wrong with your test bed If the actual number of users in the system given by Little's Law is different from the number of virtual users being pumped in by your load testing tool. i.e. if the number of users simulated by the testing tool is more than what you deduce by Little's Law, your system is probably just queuing those extra users. You'll also notice your response time will start to 'knee' once this starts to happen.

The main thing here is to do this calculation for an average of all points data points per step change in number of virtual users simulated.