Daylight Saving Time (DST) is a huge mess. For example, what is the time difference between Paris and Houston? It’s seven hours today. Yesterday it was six. A couple weeks ago it was seven.
Countries observe DST at different times or not at all. Even within one country it can be complicated. For example, the US generally observes DST. But Arizona, Puerto Rico, Hawaii, U.S. Virgin Islands, and American Samoa do not. And even within Arizona, the Navajo Nation does observe DST.
I wish everyone would take a few minutes to learn about universal time, UTC. It is essentially the time in Greenwich, England except it ignores DST. Learn how your time relates to UTC and use UTC when communicating with people who don’t share your time system. This allows, for example, a group to announce the time of a conference call in UTC and let everyone convert that to their local time. This is so much simpler than “your time”, “her time”, “his time” etc.
It’s also convenient to let people know how your time zone relates to UTC. For example, Houston time is UTC-6, i.e. six hours behind UTC. When someone asks in an email what my time zone is, maybe so they could call me during normal business hours, I may say Central Time, UTC-6. (Or in the summer, UTC-5.)
[The abbreviation UTC is an odd compromise. The French wanted to use the abbreviation TUC (temps universel coordonné) and the English wanted to use CUT (coordinated universal time). The compromise was UTC, which doesn’t actually abbreviate anything.]
Update: I’m not suggesting that people set their watches to UTC. Time zones are necessary. And if part of the world wants to have DST and another part doesn’t, vive la différence. I’m only suggesting that people use UTC when communicating with others outside their time zone.
Related post: Software engineering and alarm clocks