Most of the world sets its clocks to a whole hour ahead of or behind Greenwich. A small number of places refuse, and use a half hour or a quarter hour instead.
On a world map those offsets look eccentric — the little stripes that break the pattern, the ones scheduling software gets wrong. In practice they are the most accurate clocks on Earth.
The reason is simple. A whole-hour zone is 15 degrees of longitude wide, which is an hour of solar time. Round a country into the nearest one and you can easily end up half an hour or more from your own sun. A half-hour zone lets you aim at the meridian you actually sit on.
Here is what that looks like.
| City | Zone | Off its own sun |
|---|---|---|
| St. John's | UTC−3:30 | ~1 minute |
| Yangon | UTC+6:30 | ~5 minutes |
| Kabul | UTC+4:30 | ~7 minutes |
| Kathmandu | UTC+5:45 | ~14 minutes |
| Tehran | UTC+3:30 | a few minutes |
| Adelaide · Darwin | UTC+9:30 | modest |
| Delhi | UTC+5:30 | ~28 minutes |
| Chatham Islands | UTC+12:45 | ~31 minutes |
| Caracas (1912–65, 2007–16) | UTC−4:30 | ~2 minutes |
Now compare the countries that rounded:
| City | Zone | Off its own sun |
|---|---|---|
| Reykjavík | UTC+0 | ~90 minutes |
| Madrid | UTC+1 | ~75 minutes |
| Kuala Lumpur | UTC+8 | ~73 minutes |
| İzmir | UTC+3 | ~71 minutes |
| Dakar | UTC+0 | ~70 minutes |
The stories behind the offsets are worth having.
Nepal is the only country with a 45-minute national offset. It advanced its clocks by fifteen minutes on 1 January 1986, adopting a reference meridian at 86°15′ east — a line that runs through the peak of Gaurishankar, a sacred mountain about a hundred kilometres east of Kathmandu. The arithmetic is exact: 86.25 divided by 15 is 5.75 hours.
Newfoundland produced the most accurate clock on this site by accident of geography. UTC−3:30 is centred on the 52°30′ west meridian. St. John's sits at 52°42′ west. The city is essentially on the line. Before the Standard Time Act of 1935 there had been no agreed time in St. John's at all: some residents kept solar time, the post office kept its own version, and the wireless telegraph office ran on Eastern time. Newfoundland has since defended the half hour twice at the ballot box, in 1951 and 1963.
Afghanistan spans nearly two geographical zones and covers all of it with UTC+4:30, calculated from a meridian at about 67°30′ east. Kabul is at 69° east — within seven minutes of its own solar noon, which is more accurate than almost every city on this site.
Iran refused to round on principle. UTC+3:30 was chosen so that the national meridian at 52.5° east lands cleanly, and Iran's Solar Hijri calendar applies the same logic to the year: it has no leap-year formula at all, and begins each year at the astronomical instant of the vernal equinox.
Venezuela shows what happens when a country changes its mind. It adopted UTC−4:30 in 1912, matching the 67°30′ meridian it actually sits on. It gave that up in 1965 to conform to international whole-hour practice, took it back in 2007, and abandoned it again in 2016 during an electricity crisis. On UTC−4:30 Caracas was about two minutes from its solar noon. Today it is about twenty-eight.
So: the clocks that look wrong on the map are the ones telling the truth about where the sun is. The tidy ones are the compromise.