If there is one flaw in the late Steve Jobs’ vision of a post-PC era, it’s that the iPad and other tablet screens get disgusting and smeary after a few minutes’ use. Apart from retreating to styluses, which are anathema to modern tabletry, there’s nothing anybody can do about it. The human finger leaves a trail like a snail’s; that’s the way it is. And, as with spectacles, once you get obsessed with cleaning an iPad screen, it’s impossible for it to be too spotless – even though it’s a Sisyphean task, because as soon as you’ve degreased, you immediately start messing your screen up again.