Ready . . . Shoot . . . Aim

The change takes effect Sunday, as daylight saving time begins three weeks earlier (and ends a week later, on the first Sunday in November). And many companies are scrambling to reset BlackBerry e-mail devices, desktop PCs and big data-center computers used to automate payrolls, purchasing and manufacturing.

This puts the United States out of sync with the rest of the world for longer than usual this spring, almost certainly disrupting not only computers but also the business and travel schedules of companies, workers and travelers. Most of Europe goes to daylight saving time March 25, two weeks after America, while most of Asia, Africa and South America do not observe daylight saving time at all.

Any device that has an internal clock looms as a potential problem and must be tweaked for the time change, usually with a software patch. Most internal clocks in computing devices are programmed for the old daylight-time calendar, which Congress set in 1986.

"It's a massive amount of work to get everything in order," said Kim Stevenson, a vice president at Electronic Data Systems , a large technology services company. "And the do-nothing plan is a high-risk plan." The daylight-time shift, according to technology executives and analysts, amounts to a "mini-Y2K."

That is a reference to the rush in the late 1990s to change old software, which was unable to recognize dates in the new millennium, 2000 and beyond.