► Try the Financial Times for 4 weeks for just £1. Start your trial now - br Read more at br The FT's Martin Sandbu on what the turbulent start to January in the markets means for investors in the year ahead, after the tech leader's China sales warningbr br The FT’s Tim Bradshaw on how price differentiation may have been pushed too far, as chief executive Tim Cook blames Chinabr br ► Subscribe to FT.