according to comScore. As Facebook itself has warned, the time spent on its pages from those sitting in front of personal computers is declining rapidly because we are switching our screen time to smartphones and tablets. While smartphone minutes have doubled in a year, to 69 a month, that growth is not guaranteed to compensate for dwindling desktop usage. Facebook is the most authoritative source on its own user numbers, and the firm will update investors on its performance for the quarter. Wall Street expects revenues of about $1.44bn, up from $1.06bn in 2012. Shareholders will be particularly keen to learn how fast Facebook’s mobile user base is growing, and whether advertising revenues are increasing at the same rate. Mobile usage represented nearly a quarter of Facebook’s advertising income at the end of 2012, and the network had 680m mobile users a month in December. The company warned in recent stockmarket filings that it might be losing “younger users” to “other products and services similar to, or as a substitute for, Facebook”. Wary of competition from services that were invented for the mobile phone rather than the PC, founder Mark Zuckerberg has recently driven through a series of new initiatives designed to appeal to smartphone users. The most significant is Facebook Home, software that can be downloaded onto certain Android phones to feed news