Walk to the back of Building 18, on the edge of Facebook's new headquarters in Menlo Park, California, and you'll find the remnants of The Battle Cave. Today, this room is just another stretch of open office space, where rows of Facebookers work on who-knows-what. But if you look to your right, at the top of the wall, you'll see two metal brackets that once held a pair of flat-screen displays. That's where Joel Pobar and his crew would track their daily progress.