Real Time Is Universal

old pamphletI was on holiday in Corfu once, and happened to be in a large club one evening when the DJ made an announcement to remind people that “Greek Daylight Saving Time” was due to start and that they would have to put their watches forward by two hours before morning. This was obviously a joke, or a feeble hoax, and I ignored it. I’d signed up for a scuba expedition the next day, and when I turned up at the boat at the ungodly hour of eight a.m. I found a queue of people who’d been there since six. Gullible people.

British Summer Time ends at one in the morning next Sunday. (No, honestly, it does.) Since 1998, all European countries, including non-EU ones, have followed the same rules for changing between Summer and Winter clocks, and they all switch at the same instant. Prior to that year, there could be a week’s difference between the date on which countries switched (particularly Ireland and the UK compared to the rest of Europe), leading to complications in timetables and travel.

Actually, uniformity of time is surprisingly modern. In the British Isles prior to 1880, time was based on the actual local noon, which meant that if you got the train from London to Bristol, you had to change your watch to ten minutes later. In 1880 a law was passed to put Great Britain into a single time zone, but even then Ireland was given a separate one, at plus 25 minutes. (Dublin Mean Time was abolished in 1916, and Ireland brought into GMT. It sounds like a joke, but it isn’t.)

Britain and Ireland, and Portugal, are WET, Western European Time. Central European Time is now always exactly one hour ahead of that, Summer and Winter, and covers Europe as far East as the borders of Belarus, Bulgaria and Greece. As I mentioned, all of Europe observes the convention of changing the clocks one hour forward for Summer. But why?

The arguments in favour of a clock change in Summer are generally about shifting the working day relative to sunrise and sunset to optimise use of daylight. This is supposed to reduce energy requirements (although studies have been inconclusive) and increase road safety (ditto). In fact, laws have been made on the subject more from the point of view of vested interests and personal attitude. In the 1987 extension to Daylight Saving Time, Idaho senators voted for it based on the premise that during DST fast-food restaurants sell more french fries, which are made from Idaho potatoes. Some people object to changing the clocks “because it goes against nature” — as if there was anything natural about dividing up the day into arbitrary chunks called “hours” anyway.

On Sunday, or more likely Saturday evening, I’ll need to change the time on nine central heating thermostats and six (I think) clocks in the house. And a couple of watches. In spite of the idea of Daylight Saving Time having been around for over a century, only one of those devices has a simple way of adding or subtracting an hour. Fortunately, the computers will look after themselves. Unix-like systems, including Linux and Macs, keep their internal time in UTC, which never changes, so it’s only a matter of altering the way the time is presented to humans when BST starts or ends.

Windows systems use local time internally, including any daylight saving changes, which has often made it difficult to keep them right automatically. The title of this blog, RealTimeIsUniversal is actually a Windows Registry key, which when set, tells the computer to use UTC, not local time. It doesn’t work


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