Some who have been present on the web a little whilst might still remember one of the preeminent debugging tools: FireBug. For all its features and early praise, its author Joe Hewitt initially created it for 2 reasons: to observe what was happening on a page, pre and post resource load. Two simple metrics. A decade and change later, measuring resource loading and page performance is in equal parts proof and perception. The multitude of metrics available has allowed for granular measurements, but has also clearly created confusion. During 'The Metric System', we will learn about many of the performance metrics being bandied around like FCP, FMP, TTFB and Speed Index to name a few. But more importantly, we will see how to interpret this data, when to use it in order to extract the information our individual users need for the best user experience possible.