Time is an almost intractable problem.

bradley — Tue, 05 Jul 2005 13:17:00 GMT

I've spent a large part of my career working with time and date issues, from a project management program to a scheduling system, and there are so very many different issues to deal with that life gets really complicated for any programmer trying to make the computer understand time zones.

Here are a few surprises for the novice:

1. Time zones are not always offset by a whole number of hours. Portions of India and Canada run at offsets that are so-many-hours and a half from GMT. "Newfoundland Time" is a great search phrase to use on this.

2. Daylight Savings Time is not universal, nor universally approved of, nor universally applied.
2.1 Up until relatively recently, the switch to "British Summer Time" from GMT was made based on Naval Research by the British Admiralty, and was set by Act of Parliament on an annual basis. Diaries and calendars were printed with the date of British Summer Time marked with an asterisk, leading to the words "subject to Act of Parliament".
2.2 The state of Arizona does not observe Daylight Saving Time, except for the Navajo Reservation, which does, except for the Hopi Nation inside there, which doesn't.

3. Leap seconds exist. GMT and UTC differ by a fraction of a second, and leap seconds are used to keep that difference to a fraction less than one.

My general advice for anyone writing a program to manage dates and times would be to store every time in GMT / UTC (for most practical purposes they can be considered to be equivalent), and to convert to local time zone when displaying the time, and to convert from the local time zone when reading input. Always provide a way to specify the time zone's name, military code (a letter from A to Z) or offset from GMT, including fractional parts of hours.

re: What time is it?

bradley — Mon, 04 Jul 2005 04:13:00 GMT

I just found this utility a couple of days ago from Microsoft. It's one of their freeware utilities called Microsoft Time Zone and can be found here, http://www.microsoft.com/globaldev/outreach/dnloads/timezone.mspx

I installed it so I could keep track of the time where my sister in Germany is as well as few friends around the world. Pretty slick little utility that just sits in the system tray.