In my print column this week, I write about the numbers used to extend daylight-saving time until Sunday. You'll be turning your clock back this weekend, rather than last weekend, because of numbers from the 1970s, the last time daylight time was extended. These figures suggested that a later sunset can help conserve energy, by reducing the use of lights and other appliances in the evening. But these numbers form a flimsy basis for a major policy change, I argue, and there are no new numbers yet available to see if the experiment was successful.