Olympic organizers have unveiled a countdown clock in London's Trafalgar Square to mark 500 days until the 2012 Games.
The steel clock was revealed by four British Olympic champions: rowers Pete Reed and Andy Hodge and sailors Iain Percy and Andrew Simpson.
The clock, made by Olympic sponsor Omega, is 8.5 meters (27 feet) high, 5 meters (16 feet) long and weighs about 4 tons.
Trafalgar Square was also the location for the celebrations in London in July 2005 when the city was awarded the games.
London 2012 chairman Sebastian Coe says the clock "will be a daily and hourly reminder to everyone who visits Trafalgar Square that the countdown to the start of London 2012 has well and truly begun."
The Olympics start on July 27, 2012.