If you have been in software engineering for a while—or in fact just in the working world in general for a while—you’ve probably seen someone do something stupid with metrics. Such mistakes raise a whole bunch of interesting questions. What are the most common metrics mistakes? Why are they mistakes? Why do people make these mistakes? Are you making these mistakes? Why use metrics at all, when there are so many mistakes? In this keynote speech from the Heisenbug 2016 conference, I'll explain these mistakes, so you can avoid them.