Most of the US, Canada and Mexico’s northern border cities started Daylight Saving Time (DST) at 2 A.M. local time today. The clock “spring forward” (by shifting the clock forward) an hour, so that evenings have more daylight and mornings have less. Most of Europe will start DST on the last Sunday in March. With most of North America shifting at 02:00 local time, its zones do not shift at the same time, but increase through each time zone: EST, CST, MST, PST. Typically, clocks are adjusted forward one hour near the start of spring and are adjusted backward in autumn. The modern idea of daylight saving was first implemented during the First World War. Many countries have used it at various times since then.
DST clock shifts present other challenges. They complicate timekeeping and can disrupt meetings, travel, billing, recordkeeping, medical devices, heavy equipment, and sleep patterns. Software can often adjust computer clocks automatically, but this can be limited and error-prone, particularly when Daylight Saving Time protocols are changed. (from: Wikipedia and www.cute-calendar.com)