Windows NT Performance Monitor is one fine tool, but nothing is perfect. You may find yourself needing to look at performance information not provided in Performance Monitor. Or maybe you just think you can do better. Go for it!
Of course your plans may be a little different. You might just need to look closely at your own application's behavior in ways our program doesn't. A few API calls are provided to let you easily measure what is happening inside your application. The section "Monitoring Within an Application" at the end of this chapter covers those API calls.
Even if you do not plan to write your own performance monitor, this chapter might help you understand the tool better. Not to mention, we have first-hand knowledge that the information in this chapter makes great party conversation.