Today most consumer website visitors use their mobile phones. A slow and unresponsive experience on a mobile device can be far more offputting than a desktop experience. Such a negative experience in fact, that one of the studies cited in the presentation reveals that a painfully slow website can be more stressful than watching a horror film! So what does matter to developers and technical marketers seeking to deliver a more useful and pleasant experience to visitors? In this deck we examine user-focused performance metrics; the main front and server-side optimisation works to improve the perceived performance of our site. Which tools are best for these new performance metrics. Finally we look at some really positive results that Erudite have achieved for clients, as well as a great way to use Element Visibility in Google Tag Manager, to measure improvements to performance elements with confidence!