This article is from the source 'bbc' and was first published or seen on . It last changed over 40 days ago and won't be checked again for changes.

You can find the current article at its original source at http://www.bbc.co.uk/news/magazine-34048852

The article has changed 6 times. There is an RSS feed of changes available.

Version 0 Version 1
Who, What, Why: Why do clocks like Big Ben's run slow? Who, What, Why: Why do clocks like Big Ben's run slow?
(35 minutes later)
The chimes of Big Ben have been out by as much as six seconds. Why do public clocks go wrong, asks Nick Eardley.The chimes of Big Ben have been out by as much as six seconds. Why do public clocks go wrong, asks Nick Eardley.
The bongs of Big Ben help bring in the new year and introduce some of the best-known news programmes on British TV and radio. But chimes from the bell have been less than punctual recently.The bongs of Big Ben help bring in the new year and introduce some of the best-known news programmes on British TV and radio. But chimes from the bell have been less than punctual recently.
Radio 4's PM noticed just how slow it had become when presenter Eddie Mair brought the programme to a close. "The bong's will be any day now...." Six seconds later the first chime, supposed to start around 23 seconds before the hour, finally came. Radio 4's PM noticed just how slow it had become when presenter Eddie Mair brought the programme to a close. "The bongs will be any day now...." Six seconds later the first chime, supposed to start around 23 seconds before the hour, finally came.
"We're not absolutely 100% why it happened," says Paul Roberson, a clockmaker at the Palace of Westminster. The chimes are based on the clock's 14ft pendulum. Its movement can be affected by factors such as temperature and barometric pressure. "We're not absolutely 100% (sure) why it happened," says Paul Roberson, a clockmaker at the Palace of Westminster. The chimes are based on the clock's 14ft pendulum. Its movement can be affected by factors such as temperature and barometric pressure.
On a Monday, Wednesday and Friday the team who service it call the talking clock at five minutes before an hour, start a stopwatch and make their way up to the Grand Bell. The mechanism's hammer should then strike the bell at the moment the stopwatch hits exactly five minutes.On a Monday, Wednesday and Friday the team who service it call the talking clock at five minutes before an hour, start a stopwatch and make their way up to the Grand Bell. The mechanism's hammer should then strike the bell at the moment the stopwatch hits exactly five minutes.
The team have a tray of pre-decimal pennies, which are added or removed from the pendulum to speed it up or slow it down. Every coin adds 2/5ths of a second per day. At the moment there's about 20 pennies on the pendulum. They've been adding and taking them away for 150 yearsThe team have a tray of pre-decimal pennies, which are added or removed from the pendulum to speed it up or slow it down. Every coin adds 2/5ths of a second per day. At the moment there's about 20 pennies on the pendulum. They've been adding and taking them away for 150 years
Discrepancies, Roberson says, happen. He has known the clock to be as much as four seconds out in the past decade. Sometimes the team will have to adjust the weight of the pendulum three times a week, he says, but sometimes they can go three weeks without doing so.Discrepancies, Roberson says, happen. He has known the clock to be as much as four seconds out in the past decade. Sometimes the team will have to adjust the weight of the pendulum three times a week, he says, but sometimes they can go three weeks without doing so.
Chris McKay, a fellow of the British Horological Institute, says Big Ben "usually keeps exceptional time". "It's significantly more accurate than other [public] clocks", he adds. Chris McKay, a fellow of the British Horological Institute, says Big Ben "usually keeps exceptional time" and added: "It's significantly more accurate than other [public] clocks."
The sight of public clocks showing the wrong time is a common one around the UK. In Leicester in the 1990s, the main Victorian clock at the train station stopped telling the right time after it was disassembled and the reassembled when a rare bird was trapped inside it. In 2009, the Glasgow Evening Times estimated that five clocks in the city centre had either stopped or were telling the wrong time. The sight of public clocks showing the wrong time is a common one around the UK. In Leicester in the 1990s, the main Victorian clock at the train station stopped telling the right time after it was disassembled and then reassembled when a rare bird was trapped inside it. In 2009, the Glasgow Evening Times estimated that five clocks in the city centre had either stopped or were telling the wrong time.
By comparison Big Ben's clock is a model example. "It is very accurate," says Roberson. "It is 156 years old and has been running pretty much non-stop. If this was a steam engine it would be in a museum. It's astonishing."By comparison Big Ben's clock is a model example. "It is very accurate," says Roberson. "It is 156 years old and has been running pretty much non-stop. If this was a steam engine it would be in a museum. It's astonishing."
Subscribe to the BBC News Magazine's email newsletter to get articles sent to your inbox.Subscribe to the BBC News Magazine's email newsletter to get articles sent to your inbox.