Instrumentation may seem simple enough, but there is more to it than is usually apparent. In fact, instrumentation can even lead to an incorrect diagnosis! Let's see how this can happen.

Assume a software product has three modules: A, B, and C. The software was running slow; no one seemed to know why. So, the development manager decided it was time to instrument the code. As shown in Figure 2-1, the developers inserted simple timers into each module. When the module began, a starting time was gathered; upon exit, the finish time was gathered.

Figure 2-1. Simple instrumentation example. Each product's modules have a simple start and stop timer, providing the ability to determine the module run time.