U.S. National Debt Clock runs out of space

The National Debt Clock in New York's Times Square has run out of spaces to display $10 trillion in red ink. A trillion, by the way, is the number one followed by 12 noughts. Or, if you prefer, a thousand billion.

According to World Bank data from 2006, one trillion dollars of GDP is equivalent to 2.1 percent of the world economy and similar to the size of the Brazilian economy, which ranked 10th in the world that year.

This CNN video tells the story behind the clock. You can see an online version of the clock here.