As Lord Kelvin almost said, “To measure is to know.” But this simple dictum is surprisingly hard to follow. For it really has two meanings.
The first meaning is obvious: You cannot really know about something without measuring it. If you want to know how quickly an application works, for instance, take some key functions of the application and measure how long they take. “Good performance” is defined by the function taking less time than the acceptable threshold, and poor performance is defined by the function taking more time.
