2012 clock starts counting down as tickets go on sale

A timer showing the 500 days to go until the 2012 Olympics is being unveiled in London, but why are these countdowns so beguiling, asks John Morton, writer of comedy Twenty Twelve.

Remember Ken Livingstone's "live" running unemployment total on the old GLC building in London? Or there's the US National Debt Clock in Times Square. Or the live stock market prices and world financial indices snaking their way around the walls of the Thomson Reuters building in Canary Wharf.

There seems to be something hypnotic about watching history unfolding digitally in real time before our eyes.

But it's the clocks that count downwards towards a fixed point that really seem to have us in their thrall. How else could Countdown's 30-second analogue clock face with its plinky plonky musical accompaniment have dominated afternoon television for nearly 30 years as the procession of presenters, contestants, and fragrant letter-wranglers have come and gone beneath it.

And then there was the Millennium. Remember the mounting fear, presented to us as a kind of world-wide ticking bomb, that when the digits on our computer clocks finally flicked over to 2,000 all our planes would suddenly fall out of the sky?

And remember all those public Millennium clocks counting us down second by second through the final years, months, and days to the zero hour? The French had theirs ticking away outside the Centre Pompidou in Paris. The Queen unveiled London's at Greenwich with a thousand days to go.