As most of Europe prepares to set clocks forward an hour on March 29, millions will brace for the biannual ritual of daylight saving time (DST) . DST is mostly observed in temperate regions, where the contrast between long summer days and short winter ones makes shifting time seem useful. For newcomers to these parts of the world, DST could be bewildering at first. If you miss a meeting or arrive too early at an event, you may be gently reminded with the mnemonic: "Spring forward, fall back" —