This weekend marks the beginning of Daylight Saving Time in most parts of the United States, the first year under the new transition rules in the Energy Policy Act of 2005. Pay extra attention to your clocks this weekend. If you have a device that automatically adjusts for Daylight Saving Time, and it hasn't been updated for the new transition rules, you may end up having to adjust your clock four times this year:

  1. On March 11 (when Daylight Saving Time begins under the new rules) you have to adjust the time forward.
  2. On April 2 (when Daylight Saving Time began under the old rules) your device will automatically adjust forward, and you'll have to adjust it backward to return the clock to normal.
  3. On October 28 (when Daylight Saving Time ended under the old rules) your device will automatically adjust backward, and you'll have to adjust it forward to return the clock to normal.
  4. On November 4 (when Daylight Saving Time ends under the new rules) you have to adjust the time backward.

Okay, that's the end of the public service announcement.

I try to commemorate the Daylight Saving Time transition days by writing about time zones, and this time, it's about those time zones whose displacement from UTC is not a perfect hour multiple.

Some years ago, I was involved in a discussion over an issue that was affected by time zones. In particular, the feature in question organized its data by hour, and since the raw data format was UTC, the items were grouped by hour UTC. This works great for time zones that are an integral number of hours from GMT, but if you're in a time zone that is not, then the grouping will come out weird.

The program manager for the feature dismissed my concerns. "You're talking about those oddball time zones that are like 3½ hours from GMT? I say, tough for them. We should be optimizing for the major markets, not the fringe cases."

"Um," I replied. "One of those so-called fringe cases happens to be the second most populous country in the world."

Microsoft has already run into trouble with time zones and India. I suggested that we probably shouldn't upset them a second time.

(We also saw earlier that India doesn't group digits in threes.)