Vice President Joe Biden and U.S. Rep. Paul Ryan meet at 8 tonight in Danville, Ky., for their only debate.

Because Republican Mitt Romney is widely believed to have won the first presidential debate, the pressure on Biden to turn in a good performance for the Democrats has grown.

Biden's debating skills have been, well, debated. He's committed several gaffes in campaign speeches, but he's thought to have done well against former Alaska Gov. Sarah Palin in their meeting four years ago.

At the same time, Ryan faces some pressure as well. It's the biggest stage he's ever faced, and his own economic proposals are at odds with some of Romney's.

So how can a voter keep score? Click the graphic at the right.