Reader Zorro writes: The mania for "flat" user interfaces is costing publishers and e-commerce sites billions in lost revenue. A "flat" design removes the distinction between navigation controls and content. Historically, navigation controls such as buttons were shaded, or given 3D relief, to distinguish them from the application or web page's content. The mania is credited to Microsoft with its minimalistic Zune player, an iPod clone, which was developed into the Windows Phone Series UX, which in turn became the design for Windows from Windows 8 in 2012 onwards. But Steve Jobs is also to blame. The typography-besotted Apple founder was fascinated by WP's "magazine-style" Metro design, and it was posthumously incorporated into iOS7 in 2013. Once blessed by Apple, flat designs spread to electronic programme guides on telly, games consoles and even car interfaces. The consequence is that users find navigation harder, and so spend more time on a page. Now research by the Nielsen Norman Group has measured by how much. The company wired up 71 users, and gave them nine sites to use, tracking their eye movement and recording the time spent on content. On average participants spent 22 per cent more time (i.e. slower task performance) looking at the pages with weak signifiers," the firm notes. Why would that be? Users were looking for clues how to navigate. "The average number of fixations was significantly higher on the weak-signifier versions than the strong-signifier versions. On average, people had 25 per cent more fixations on the pages with weak signifiers."