This Sunday 29th March, the much awaited passing of winter is confirmed with the changing of the clocks. The beginning of British Summer Time in the UK is jump-started with the loss of one hour at 1am, during the wee small hours of Sunday morning. However, with our increased dependence on smartphone automation most of us probably won’t notice the difference: our trusted tech tools will keep us on time. While the changing of time won’t be a major consideration for most people, it poses unique challenges for anyone concerned with IT or tech and should be handled correctly. If that’s you then here’s what you need to know about BST.

1. What Happens To Scheduled Updates During The ‘Lost Hour’?

When clocks go forward in the spring, there’s an hour of time in the middle of the night that gets skipped. When clocks go back in the autumn there’s an hour that happens twice. If a computer is scheduled to do something during this hour, for example, run a backup or carry out a daily update such as giving out free credits in a free-to-play game, then you risk either that the task doesn’t happen or that it happens twice. Either outcome could be bad.

Even if you don’t have anything scheduled during the “missing” or “repeated” hour, you can, if you’re not careful, end up with other sorts of errors. For example, let’s say you’ve got a countdown to something happening on the day after the clocks change. You don’t want the countdown to be out by an hour do you? To avoid these unplanned mishaps, you should carry out explicit tests to ensure that systems behave correctly before, during, and after a daylight-savings time change. Similarly, run a test to make sure that sane things happen on 29 February in a leap year! The next one is in 2016, so there’s plenty of time to prepare for this.

2. Handling Time

There are lots of different ways of handling time on computer systems. Many systems, even in different time zones from the UK, do everything by reference to GMT or, more formally, UTC or “Coordinated Universal Time.” Further, the majority of systems “translate” into local time (including making any daylight savings time adjustments) only when it comes to displaying the time to people. Other systems do even stranger things, such as recording time as “number of seconds since the beginning of the day on 1 January 1970” – which is why, in computing circles, you’ll hear that date referred to as the “Unix Epoch” or sometimes just “the epoch”.

This counting seconds since the epoch makes some things easier for the computer – e.g. it knows 11:30:23 on 6 March 1997 is before 10:28:59 on 1 November 2001 just because the former represented as a smaller (but still very big) number than the latter. Again, dates and times stored as “milliseconds since the epoch” are converted to a more human-friendly form only when they need to be shown to humans! Even for computers though, this can cause problems – from the difficulty of storing old dates (which is why it’s hard to put dates from before the 20th century in an Excel for instance) to the “Year 2038 problem” (which is a potential future version of the Y2K problem).

3. Blink & You’ll Miss It

As if losing or gaining hours wasn’t causing enough of a technical headache for IT and tech professionals, in certain areas of computing, you also have to worry about “leap seconds” and the different time systems used in specific technologies. Leap seconds are pretty fascinating: so much so that they have an enthusiastic fan base of “tech-nuts” and their own dedicated website. Leap seconds are added to time because the Earth’s rotation is very – well extremely – gradually slowing down. In practice they don’t really affect us that much and in order to see one pass you need to plan and pay very close attention.

You can’t catch a leap second looking at an analogue clock, nor can you see one pass before your eyes on a PC or laptop clock, or any standard clock you’d find on your commute – and you most definitely won’t see one looking at a sun dial. Bizarrely, however, you’re more likely to see a leap second online, using a web cam, viewing a still or movie camera, looking at an eBay auction item ending at 23:59:06 or using a kinemetrics clock. If you don’t have time for that sort of sport you can see some pre-recorded leap seconds pass here.

As if leap seconds weren’t mind-boggling enough, there’s the difference between “Coordinated Universal Time” and “International Atomic Time,” which is different again from the time used in GPS sat nav systems. It’s true that, in practice, these tiny time corrections do not really affect us. But there’s lots of fun stuff to read about this online.

Unless you use the clocks that tick and are in charge of IT systems at work, it’s likely that you won’t notice the loss of one hour at all. All you need to know about the changing of the clocks this weekend is that in the UK the clocks go forward one hour on the last Sunday in March bringing us more daylight in the evenings and less in the mornings. In simple terms – you’ll find it easier to skip out of work in the evenings but even harder to get out of bed in the mornings! And remember to change those old manual clocks that won’t auto-update!