Greenwich Mean Time

An Eccentric Anomaly: Ed Davies's Blog

OK, explain this to me: WTF are programmers so bad at telling the time?

This morning the UK sprang forward so I find the following on my Android phone:

In case it's not obvious, that's the main screen of the clock app and the configuration screen for the “world” times below the main local-time display. What's wrong with them? Enough to form a teachable moment or two.


First of all, GMT is an old and poorly defined timescale which nobody uses in practice any longer, despite the fact that UK legislation still pretends we do. It's probably best to consider it an old name for UT1.

All timezones in widespread use are specified by reference UTC which is a timescale defined by atomic clocks with tweaks (leap seconds since 1972) added to keep it aligned approximately (within 0.9 seconds) with UT1. Since this has been the case for over 50 years it's well past time to simply drop the term “GMT” and just use “UTC” in all common cases.

GMT vs UK Time

More substantially, there's the relatively widespread problem of confusion between GMT (i.e., UTC) and whatever the civil time happens to be the UK at any given instant. It's a long time since I've used Microsoft Windows but it was notorious for this.

For the US east coast there are three commonly used timezone abbreviations: EST: eastern standard time, winter time; EDT: eastern daylight time, summer time; and ET: eastern time, whichever of the first two happens to be in force at the instant in question. Part of the problem is that there's no equivalent of ET for UK time so it's not surprising that some of the majority who don't pay much attention to such things think using GMT is appropriate.

However, the mess Android has made of it here is really quite special.

What I intended the clock app to show is current UK civil time as the main display with UTC and US east coast time below it. This is, indeed, what gets displayed but the labelling is just bizarre.

I can't remember what the labelling was when I set it up but to suddenly mark a GMT/UTC time (GMT+00:00) as “British Summer Time” is quite inexplicable. Why is this stuff so difficult?

Bonus Rant

While we're on the subject, if we really have to mess with the clocks twice a year, which I doubt, can we at least all change on the same date?

In the early 1980s I worked for a UK company in the Netherlands. At that time the UK and the Netherlands changed at different times so there were a confusing couple of weeks at each end of the year when the usual 1-hour offset didn't apply. Since 1996, though, all EU countries which observe summer time switch on the last Sundays in March and October.

Up to and including 2006 the US changed on the first Sunday in April and the last Sunday in October. Starting with 2007 they've been changing on the 2nd Sunday in March and first Sunday in November extending DST by 5 weeks, or so.

Since the energy and safety benefits of changing at all are so marginal it seems weird to me that anybody thinks it'll make much difference exactly when the change is made. If they'd wanted to extend DST a bit it seems to me that it would have been better for the US to have done so by only one week by aligning it with the EU.

Obviously, you'd finish up with a few hours when the offset would be different but that's unlikely to matter anything like as much for practical purposes.