It's 1:30 and 36 seconds. Ian Westworth knows this for certain, because that's the time it says on 14 clock faces and three digital clock readouts on a master control panel in the Clock Makers Workshop, his office beneath Westminster Palace. In charge of keeping 500 clocks in Parliament ticking, some of them priceless antiques, he has already made his rounds winding and checking the accuracy of one timepiece after another.

Time matters deeply, dearly and daily to Westworth, 43, a barrel-chested former rugby player who is also a member of a guild called the Worshipful Company of Clockmakers, founded by royal charter in 1631. "I hate being late," he says in his basement workshop, where dozens of clocks are incessantly ticktocking, a testament to his tools: pin vices, tiny files and patience.

It's Wednesday afternoon. That means it's time to wind, pamper and putter with the clock that matters most of all to England: Big Ben.

Though the whole clock tower is commonly called Big Ben, Westworth explains, Big Ben is actually the bell that hangs in the tower above the famous clock faces. The Great Westminster Clock, as it is officially known, triggers the hammer that strikes Big Ben, which weighs more than 13 tons. Its sonorous BONG has been London's time-check for a century and a half.

"Time to go up," Westworth says, pulling his office door shut and walking through the narrow passageways that lead to the foot of the 316-foot clock tower. As he climbs the spiral staircase, he stops for a breather a third of the way up the 290 steps, ducking into a room where ill-behaving members of Parliament used to be imprisoned.

"Don't talk about the heat," he says. It's 90 degrees outside, just like it was one day in May when the clock inexplicably stopped for 90 minutes and had to be reset, making headlines around the world.

Heading up the narrow stairwell, he arrives at his destination, the Clock Tower Mechanism Room. His Casio wristwatch says 1:44:14. Three times a week he climbs up here to wind and tend to the inner workings of the clock, an impressive, black, five-ton mechanism with flywheels and fan belts and widgets that is now ticking and tocking no louder than a grandfather clock. Then suddenly things go all Willy Wonka. Two great sheets of black metal, which look like huge fly swatters, twist on their axle, and things start clanking and banging. Then the payoff: The quarter-hour chimes of the four smaller bells that flank Big Ben begin their melodious magic.

"I have a sense of awe," Westworth says. "I'm looking after Britain's best-known clock, if not the world's."

But 1:46:12 on winding day is no time to dawdle. He pushes a button and a 2.5-horsepower engine screams to life and begins pulling 150 feet of steel cable that suspends two weights, each over a ton. Gravity acting on those weights turns the gears needed to clang Big Ben and the other bells, and three times a week they need to be hoisted back up.

The clock itself needs to be wound by hand, so Westworth grabs an 18-inch-long winch-arm, affixes it to a nut and starts turning. "Otherwise, it would stop," he says.

At 1:57:50, Westworth picks up a phone in the clock room. He dials 1-2-3 and checks in with the digitized voice that reads out Britain's official time. At precisely 1:58:00, he synchronizes his red, solar-powered, digital stopwatch, then climbs 44 more steps to the belfry. He waits alongside Big Ben, the giant bell that has gone green from age and the slashing London rain.

With a sudden swift smack from a huge iron hammer, Big Ben speaks. Westworth frowns.

"We're a half-second fast," he says. But he knows how to fix that.

All it will take is a single coin, he says, climbing back down to the clock room. He reaches in a cupboard for a British halfpenny, now out of circulation, and explains that if he replaces one of the nine larger coins on the clock's pendulum with this smaller one, the imperfection will be erased. He jots down the problem and his remedy in a ledger, then rounds out the hour examining mischievous bevel gears and every bolt and bearing.

At the end of the day, when he leaves the ticktock of hundreds of timepieces at work, he will ride home on his motorcycle to a house with no clocks. "For years I have been looking for the perfect clock," he says. "I just haven't found the right one."

It's 3:00 and Big Ben rings out again. Westworth checks the tower's famous opal glass clock faces with their 14-foot-long minute hands. He stands in a narrow passageway inside them, unseen by the hundreds of admiring tourists below.

Ian Westworth winds the Great Westminster Clock. His job is to make sure the 500 clocks in Parliament are accurate.

The clock inexplicably stopped for 90 minutes in May and had to be reset.