Ireland and the UK Aren’t In The Same Timezone!

This weekend, while investigating a bug in some code that generates iCalendar (ICS) feeds, I learned about a weird quirk in the Republic of Ireland’s timezone. It’s such a strange thing (and has so little impact on everyday life) that I imagine that even most Irish people don’t even know about it, but it’s important enough that it can easily introduce bugs into the way that computer calendars communicate:

Most of Europe put their clocks forward in Summer, but the Republic of Ireland instead put their clocks backward in Winter.

If that sounds to you like the same thing said two different ways – or the set-up to a joke! – read on:

Map showing timezones of Europe. The UK and Ireland are grouped (along with Iceland) in a zone labelled as being UTC+0.
The timezones of Europe look pretty simple compared to some parts of the world, but the illustration of the British Isles hides an interesting eccentricity.

A Brief History of Time (in Ireland)

Poster titled "Time (Ireland) Act 1916", advising that "On and after Sunday 1st October 1916 Western European Time will be ovserved throughout Ireland" asking people to set their clocks and watches back 35 minutes.
Spring forward, fall back… just a little bit back, though. Not too much.

After high-speed (rail) travel made mean solar timekeeping problematic, Great Britain in 1880 standardised on Greenwich Mean Time (UTC+0) as the time throughout the island, and Ireland standardised on Dublin Mean Time (UTC-00:25:21). If you took a ferry from Liverpool to Dublin towards the end of the 19th century you’d have to put your watch back by about 25 minutes. With air travel not yet being a thing, countries didn’t yet feel the need to fixate on nice round offsets in the region of one-hour (today, only a handful of regions retain UTC-offsets of half or quarter hours).

That’s all fine in peacetime, but by the First World War and especially following the Easter Rising, the British government decided that it was getting too tricky for their telegraph operators (many of whom operated out of Ireland, which provided an important junction for transatlantic traffic) to be on a different time to London.

1885 GPO telegraph instrument from the Porthcurno Telegraph Museum, which Dan almost visited the other week but it was closed.
It’s widely believed that the world’s first “U UP? [STOP]” message never got a response as a direct result of Anglo-Irish timezone confusion.
So the Time (Ireland) Act 1916 was passed, putting Ireland on Greenwich Mean Time. Ireland put her clocks back by 35 minutes and synched-up with the rest of the British Isles. And from then on, everything was simple and because nothing ever went wrong in Ireland as a result of the way it was governed by by Britain, nobody ever had to think about the question of timezones on the island again.

Ah. Hmm.

December 1920 photograph showing St Patrick's Street, Cork, following the burning of the city by British forces.
“Those Irish people want to govern their own country, do they? After we so kindly shared our king with them? Right-ho: let’s set fire to their cities and see how they feel then.”

Following Irish independence, the keeping of time carried on in much the same way for a long while, which will doubtless have been convenient for families spread across the Northern Irish border. But then came the Second World War.

Summers in the 1940s saw Churchill introduce Double Summer Time which he believed would give the UK more daylight, saving energy that might otherwise be used for lighting and increasing production of war materiel.

Ireland considered using the emergency powers they’d put in place to do the same, as a fuel saving measure… but ultimately didn’t. This was possibly because aligning her time with Britain might be seen as undermining her neutrality, but was more likely because the government saw that such a measure wouldn’t actually have much impact on fuel use (it certainly didn’t in Britain). Whatever the reason, though, Britain and Northern Ireland were again out-of-sync with one another until the war ended.

Newspaper clipping advising that "Double Summer Time comes to an end on Saturday night, August 8-9, when all clocks and watches should be put back one hour, thus reverting to British Summer Time, which will probably be maintained throughout the winter."
I like to imagine that the development of powerful computers by the folks at Bletchley Park was a result of needing to keep track of timezones across the British Isles.

From 1968 to 1971 Britain experimented with “British Standard Time” – putting the clocks forward in Summer once, to UTC+1, and then leaving them there for three years. This worked pretty well except if you were Scottish in which case you’ll have found winter mornings to be even gloomier than you were used to, which was already pretty gloomy. Conveniently: during much of this period Ireland was also on UTC+1, but in their case it was part of a different experiment. Ireland were working on joining the European Economic Community, and aligning themselves with “Paris time” year-round was an unnecessary concession but an interesting idea.

But here’s where the quirk appears: the Standard Time Act 1968, which made UTC+1 the “standard” timezone for the Republic of Ireland, was not repealed and is still in effect. Ireland could have started over in 1971 with a new rule that made UTC+0 the standard and added a “Summer Time” alternative during which the clocks are put forward… but instead the Standard Time (Amendment) Act 1971 left UTC+1 as Ireland’s standard timezone and added a “Winter Time” alternative during which the clocks are put back.

Two clocks, both showing the same time. One has a sign reading "LONDON", the other "DUBLIN, I GUESS?"
It all seems so simple until you actually think about it.

(For a deeper look at the legal history of time in the UK and Ireland, see this timeline. Certainly don’t get all your history lessons from me.)

So what?

You might rightly be thinking: so what! Having a standard time of UTC+0 and going forward for the Summer (like the UK), is functionally-equivalent to having a standard time of UTC+1 and going backwards in the Winter, like Ireland, right? It’s certainly true that, at any given moment, a clock in London and a clock in Dublin should show the same time. So why would anybody care?

Perl Data::ICal::TimeZone implementation of Dublin timezone, incorrectly showing summer DST at +1 rather than winter DST of -1.
This code for Europe/Dublin, from the Perl module Data::ICal::TimeZone, is technically-incorrect because it states that the winter time is the standard and daylight savings of +1 hour apply in the summer, rather than the opposite.

But declaring which is “standard” is important when you’re dealing with computers. If, for example, you run a volunteer rota management system that supports a helpline charity that has branches in both the UK and Ireland, then it might really matter that the computer systems involved know what each other mean when they talk about specific times.

The author of an iCalendar file can choose to embed timezone information to explain what, in that file, a particular timezone means. That timezone information might say, for example, “When I say ‘Europe/Dublin’, I mean UTC+1, or UTC+0 in the winter.” Or it might say – like the code above! – “When I say ‘Europe/Dublin’, I mean UTC+0, or UTC+1 in the summer.” Both of these declarations would be technically-valid and could be made to work, although only the first one would be strictly correct in accordance with the law.

Stressed programmer hunched over a MacBook. Photo by Anna Shvets from Pexels.
Clients who need solid timezone support represent 50% of a programmer’s production of stress hormones. See also Falsehoods Programmers Believe About Time.

But if you don’t include timezone information in your iCalendar file, you’re relying  on the feed subscriber’s computer (e.g. their calendar software) to make a sensible interpretation.. And that’s where you run into trouble. Because in cases like Ireland, for which the standard is one thing but is commonly-understood to be something different, there’s a real risk that the way your system interprets and encodes time won’t necessarily be the same as the way somebody else’s does.

If I say I’ll meet you at 12:00 on 1 January, in Ireland, you rightly need to know whether I’m talking about 12:00 in Irish “standard” time (i.e. 11:00, because daylight savings are in effect) or 12:00 in local-time-at-the-time-of-the-meeting (i.e. 12:00). Humans usually mean the latter because we think in terms of local time, but when your international computer system needs to make sure that people are on a shift at the same time, but in different timezones, it needs to be very clear what exactly it means!

And when your daylight savings works “backwards” compared to everybody else’s… that’s sure to make a developer somewhere cry. And, possibly, blog about your weird legislation.

Dan Q found GC4PV7E BFG #3– The Black Hairstreak

This checkin to GC4PV7E BFG #3– The Black Hairstreak reflects a geocaching.com log entry. See more of Dan's cache logs.

I first came to this series in 2014 – seems like a lifetime ago! – but got called away by something (a problem with the beta of Three Rings‘ Milestone: Promethium) before I could find more than the first one. Today, under our recently reduced lockdown and in an effort to save the kids from crawling to the walls, we came out for a walk along this side of the woods and quickly found this cache. TFTC!

Map of 51.79475,-1.116633

Dan Q found GC64QG0 Post Post SN4 309 (Alex Park)

This checkin to GC64QG0 Post Post SN4 309 (Alex Park) reflects a geocaching.com log entry. See more of Dan's cache logs.

After a quick pre-breakfast expedition to the (very good, but under-visited) nearby cache GC18GJB, I decided to take a minor diversion on my way back to Alexandra House via this little cache. An easy find, although I did for a moment think I might have been being watched… only to discover that the creature watching me was a deer. Does a deer count as a muggle? TFTC.

Map of 51.510583,-1.766783

Dan Q found GC18GJB Twelve O’Clock High

This checkin to GC18GJB Twelve O'Clock High reflects a geocaching.com log entry. See more of Dan's cache logs.

An abundance of leaf mulch made it more–challenging than I’d anticipated both to reach the GZ, on account of slipperiness, and to find the container, on account of camouflage. My geosense took me directly to the right spot but after an initially fruitless search I expanded my radius. Then, still having had no luck, I checked the hint and returned to the site of my initial hunch for a more-thorough search. Soon, the cache was in my hand. SL, TNLN.

Like many previous finders I’m staying in the nearby Alexandra House. My fellow volunteers and I at a nonprofit we run were getting together for our AGM and a Christmas meal (I know it’s early in the year for such things, but among our activities was signing Christmas cards to the hundreds of charities we support, and we have to catch the last international posting dates!).

As has become my tradition at our get-togethers, I got up for a quick hike/geocaching expedition before breakfast. I’m glad I did! This under-hunted cache represents much of what’s best about the activity: a decent sized container, maintained for many years, in a location that justifies a nice walk. FP awarded.

Side note: there’s a bus stop (pictured) at the North end of this footpath. Who’s it for??? In the middle of nowhere with a two-hourly bus five days a week, it doesn’t seem to be serving anybody! Maybe a geocacher will disembark there, someday.

Bus stop attached to a lamppost on a misty, empty road.
Bus stop in the middle of nowhere

TFTC.

Map of 51.505883,-1.77865

Dan Q found GC5MYFN 01 It’s a Bugs Life x2

This checkin to GC5MYFN 01 It's a Bugs Life x2 reflects a geocaching.com log entry. See more of Dan's cache logs.

Some fellow volunteers and I are on an “away weekend” in the forest; this morning before our first meeting I lead a quick expedition of both established and first-timer geocachers around a few of the local caches.

Passed another couple of ‘cachers on the way from GC840TN, but it sounded like they’d been having less luck than us this morning. Coordinates spot on; dropped me right on top of the cache and I was familiar with this kind of container so I picked it up as soon as I got there – quick and easy find, and our last for the morning! TFTC.

Map of 52.420517,0.86445

Dan Q found GC840TN Georassic Diplodocus

This checkin to GC840TN Georassic Diplodocus reflects a geocaching.com log entry. See more of Dan's cache logs.

Some fellow volunteers and I are on an “away weekend” in the forest; this morning before our first meeting I lead a quick expedition of both established and first-timer geocachers around a few of the local caches.

Coordinates didn’t put us very close: perhaps because of tree cover interfering with the GPSr; we needed to decipher the hint. The hint was good, though, and I went straight to the dino’s hiding place, trampled past a few fresh nettles, and retreived it. Excellent caches; we loved these!

Map of 52.42,0.8682

Dan Q found GC5MYFW 02 It’s a Bugs Life x2

This checkin to GC5MYFW 02 It's a Bugs Life x2 reflects a geocaching.com log entry. See more of Dan's cache logs.

Some fellow volunteers and I are on an “away weekend” in the forest; this morning before our first meeting I lead Ga quick expedition of both established and first-timer geocachers around a few of the local caches.

Geoff pounced right onto this one, stunning some of our less-experienced ‘cachers who’d never considered the possibility of a container like this!

Map of 52.420083,0.871617

Dan Q found GC3JG9P Georassic – Stegosaurus

This checkin to GC3JG9P Georassic - Stegosaurus reflects a geocaching.com log entry. See more of Dan's cache logs.

Some fellow volunteers and I are on an “away weekend” in the forest; this morning before our first meeting I lead a quick expedition of both established and first-timer geocachers around a few of the local caches.

Our tagalong 5-year-old and 2-year-old co-found this one; they were pretty much an ideal size to get to the GZ. This was the last of the three caches they attended; they went back to their cabin after this but most of the adults carried on.

Map of 52.418433,0.873267

Dan Q found GC840T0 Georassic Parasaurolophus

This checkin to GC840T0 Georassic Parasaurolophus reflects a geocaching.com log entry. See more of Dan's cache logs.

Some fellow volunteers and I are on an “away weekend” in the forest; this morning before our first meeting I lead a quick expedition of both established and first-timer geocachers around a few of the local caches.

So THAT is what a Parasaurolophus looks like! Swiftly found by our tame 5 year-old, who was especially delighted to pull a dinosaur out of its hiding place.

Map of 52.417917,0.8694

Dan Q found GC3JG92 Georassic – Spinosaurus

This checkin to GC3JG92 Georassic - Spinosaurus reflects a geocaching.com log entry. See more of Dan's cache logs.

Some fellow volunteers and I are on an “away weekend” in the forest; this morning before our first meeting I lead a quick expedition of both established and first-timer geocachers around a few of the local caches.

After a bit of an extended hunt (this dino was well-hidden!) we found this first container; delighted by the theming of this series; FP awarded here for the ones we found.

Map of 52.417733,0.8651

My TED Video on the Future of Work

This article is a repost promoting content originally published elsewhere. See more things Dan's reposted.

I was thrilled to participate in TED’s new video series, The Way We Work, and not surprisingly I made the case that distributed work is where everything is headed.

Like Automattic (Matt’s company), Three Rings has also long been ahead of the curve from a “recruit talent from wherever it is, let people work from wherever they are” perspective. Until I was recently reading (more than I had previously) about the way that Automattic “works” I was uncertain about the scalability of Three Rings’ model. Does it work for a commercial company (rather than a volunteer-run non-profit like Three Rings)? Does it work when you make the jump from dozens of staff to hundreds? It’s reassuring to see that yes, this kind of approach certainly can work, and to get some context on how it does (in Automattic’s case, at least). Nice video, Matt!

Programming is just solving puzzles

This article is a repost promoting content originally published elsewhere. See more things Dan's reposted.

‘Programming is just solving puzzles’ – Nominet (Nominet)

As a child, I wanted to be a botanical researcher. I loved being outdoors and used to visit the botanical gardens near my house all the time. My grandma inspired me to change my mind and helped me get interested in science. She lived in the country and we would look at the stars together,…

Ruth Trevor-Allen

As a child, I wanted to be a botanical researcher. I loved being outdoors and used to visit the botanical gardens near my house all the time. My grandma inspired me to change my mind and helped me get interested in science. She lived in the country and we would look at the stars together, which led to an early fascination in astronomy.

Unusually for the era, both my grandmothers had worked in science: one as a lab technician and one as a researcher in speech therapy. I have two brothers, but neither went into technology as a career. My mum was a vicar and my dad looked after us kids, although he had been a maths teacher.

My aptitude for science and maths led me to study physics at university, but I didn’t enjoy it, and switched to software engineering after the first year. As soon as I did my first bit of programming, I knew this was what I had been looking for. I like solving problems and building stuff that works, and programming gave me the opportunity to do both. It was my little eureka moment.

Wise words from my partner on her workplace’s blog as part of a series of pieces they’re doing on women in technology. Plus, a nice plug for Three Rings there (thanks, love!).

Dan Q found GC1H3PK Keep On Mooving

This checkin to GC1H3PK Keep On Mooving reflects a geocaching.com log entry. See more of Dan's cache logs.

Some fellow volunteers and I were staying at nearby Wroxall Abbey following our Christmas party this weekend and I took the opportunity to walk out here between breakfast and check-out to hunt for this cache. Passing GC5RZB4 (and a herd of cows) on the way I was soon able to spot the tell-tale signs of a cache hiding place and soon had the container in my hand.

I love to see a good location with a week maintained cache; nice work CO, and TFTC!

Map of 52.33565,-1.6792