With our mobile phones always at hand, we are depending less and less on other timekeeping devices. The wristwatch, once a necessity of life, has become an affordable fashion accessory to some and an expensive luxury item to others. Thankfully, the wall clock has not yet gone out of fashion, remaining easier to consult than bringing our phones out of our pockets or handbags. Representational Image. Clocks have long been a feature of puzzles, some of which have appeared in Problematics over the last couple of years. But there are plenty more of them. Both of this week’s puzzles involve clocks, and come from illustrious sources. The first one, in particular, is of a unique kind. #Puzzle 116.1 The late Martin Gardner, the American writer of popular mathematics who introduced readers to puzzles from around the world, also created some diversions himself. The following trick is one of Gardner’s own. It begins, like so many mathematical tricks, by asking someone to think of a number. In this case, Gardner suggests, let the number be less …