How Does Big Ben Keep Accurate Time?

Inside this iconic clock tower hangs Big Ben itself. The nearly 14-ton bell that gives the tower its nickname. The bells that chime on the quarter hour sit around it. Their strikes are controlled by the intricate ticking mechanism at the heart of the tower. It keeps the clock accurate to within just two seconds a week. On each side, 312 shards of opal glass make up the clock face. The copper minute hands are 14 feet long, as tall as a double-decker bus. These famous dials have kept London running on time for 160 years. Like any ordinary wristwatch, this clock needs winding, just as it did in Victorian times. Put the winding handle on and then winding for about the next hour and a half. When Parliament commissioned this clock in 1854, they insisted Big Ben be the biggest, most powerful chiming clock in the world. And most challenging for the designers, accurate to within two seconds per week. Ian checks if Big Ben is on time. He gets an accurate reading of Greenwich Mean Time and then heads to the belfry. It's currently almost 10 a.m. Will Big Ben chime on time? So what you'll see, this is the first hammer that moves. So it doesn't come as a shock. If you watch that one, it'll lift up and drop and play the 16 notes. Then there's a pause of about 10 seconds and then that one will go. It'll be any moment now. Big Ben's chime roars across the capital at 118 decibels, almost as loud as a jet plane taking off. So is the clock on time? We're one second slow. Traditionally what we do, we add a penny. One penny, old pre-decimal coin, speeds the clock up just to bring the clock back into time. Like those original clock keepers, Ian knows this tiny weight raises the pendulum's center of gravity and makes it swing faster. We've corrected it and it's come back up to time. That's pretty good for 160 year old clock.