Is it plugged in?

Debugging: The 9 Indispensable Rules for Finding Even the Most Elusive Software and Hardware Problems, by David J. Agans, Amacom (www.amacombooks.org), 2002. 184 pages. $21.95.In this informal, highly readable treatise, David Agans details nine steps you can take to uncover design errors or locate field failures. I won't list them here, but indeed "check the plug" is one. In sections dubbed "war stories," Agans describes the application of his nine rules to everything from programmable gate arrays to hot-water systems. Agans, an MIT graduate and computer systems consultant, urges you to understand the system you're debugging, even if it means reading the manual. Of course, you can't debug something that doesn't seem broken, so he describes ways to induce intermittent failures.

Cogitation can be debug's enemy, Agans advises. So, although to engineers thinking beats working every time, it's important to "quit thinking and look." To help you determine where to look, he suggests you narrow your search for bugs, focusing on noisy signals, for instance. And, of course, replace only one component at a time, keeping track of what you've done. (Write it down!) If all else fails, talk over the problem with a friend or colleague. And, he admonishes, "If you didn't fix it, it ain't fixed"—and don't assume your fix has worked, test it.

Well, I have mentioned all nine rules after all. But get this book. Its stories and examples are amusing and instructive. If you master the rules, writes Agans, you can be a hero, or at least leave work on time and get a good night's sleep.