The National Debt Clock constantly updates to show the current United States gross national debt by billboard-sized running total dot-matrix display. In Manhattan, New York City, Times Square Debt Clock is currently installed on Sixth Avenue (Avenue of the Americas). The National Debt Clock in New York has run out of digits to record the spiraling figure due to US governments debts have ballooned so badly.

New York real estate developer Seymour Durst wanted to highlight the rising national debt so he sponsored the installation of the first clock in 1989.

The national debt remained under $3 trillion but was rising at the time and from 2000 to 2002, the clock was temporarily switched off due to the debt actually falling during that period.

The current clock replaces and dismantles the original clock in 2004 at the new location one block away. For the first time, the U.S. national debt exceeded $10 trillion in 2008, leading to press reports that the clock had run out of digits. The digital dollar sign has been replaced with a cheaper, non-digital version to make room for the extra number, as a temporary solution. According to AP, the Durst Organization which designed the clock, plans to add two more digits to the sign in the near future to make room for a quadrillion dollar amount.

Source: http://en.wikipedia.org/wiki/National_Debt_Clock