To improve software developers' productivity has been the holy grail of software engineering research. But before we can claim to have improved it, we must first be able to measure productivity. This is far from trivial. In fact, two separate research lines on software engineers' productivity have co-existed almost in complete isolation for a long time: automated product and process measures on the one hand and self-reported or perceived productivity on the other hand. In this article, we bridge the gap between the two with an empirical study of 81 software developers at Microsoft.