WASHINGTON (Agencies) - Millions of Americans will vote on Tuesday (today) to elect a new president and will encounter an unfamiliar low-tech landscape at the polls as well. The focus will be on 11 states that will determine the next occupant of the White House. Unlike the other 41 states that are already firmly behind specific candidates, these 11 can be won by either Democrat Barack Obama or Republican John McCain. That explains why they are called swing or battleground states. The 11 battleground states are Indiana, Virginia, West Virginia, North Carolina, Ohio, Missouri, Pennsylvania, Florida, New Hampshire, Colorado and Nevada. With a combined 141 electoral college votes, the swing states are a must-win for either candidate. That explains why Obama and McCain have spent the last weeks campaigning in these states. Past elections illustrate the importance of swing states. In 2000, Republican George Bush edged out Democrat Al Gore after beating him by about 500 votes in Florida to carry the state's 25 electoral college votes. In 2004, Bush defeated Democrat John Kerry but that time, the crucial swing state was Ohio. About half of all voters will vote in a way that is different from what they did in the last presidential election, and most will use paper ballots rather than the touch-screen machines that have caused concern among voting experts. But the change does not guarantee a smooth election day, as the nation's voting system remains untested for what is expected to be an unprecedented turnout. Six years after the largest federal overhaul in how elections are run, voting experts are still predicting machine and ballot shortages in several swing states and late tallies on election night. Two-thirds of voters will mark their choice with a pencil on a paper ballot that is counted by an optical scanning machine, a method considered far more reliable and verifiable than touch screens. But paper ballots bring their own potential problems, voting experts say. The scanners can break down, leading to delays and confusion for poll workers and voters. And the paper ballots of about a third of all voters will be counted not at the polling place but later at a central county location. That means that if a voter has made an error - not filling in an oval properly, for example, a mistake often made by the kind of novice voters who will be flocking to the polls - it will not be caught until it is too late. As a result, those ballots will be disqualified. Obama was leading McCain in six of eight key battleground states, including the big prizes of Florida and Ohio, according to a series of polls released on Monday. Obama holds a 7-point edge over McCain among likely US voters in a separate C-SPAN/Zogby national tracking poll, up one percentage point from Sunday. The telephone poll has a margin of error of 2.9 percentage points. Obama heads into Tuesday's voting in a comfortable position, with McCain struggling to overtake Obama's lead in every national opinion poll and to hold off his challenge in about a dozen states won by President George W Bush in 2004. The new state polls showed Obama with a one-point lead in Missouri and two-point lead in Florida, within the margin of error of 4.1 percentage points. But Obama also holds leads in Ohio, Virginia and Nevada - all states won by Bush in 2004. The five states where Obama is ahead have a combined 76 electoral votes. Along with states won by Democrat John Kerry in 2004, they would give Obama 328 electoral votes " far more than the 270 needed to win the White House. Obama also leads by 11 percentage points in Pennsylvania, which McCain has targeted as his best chance to steal a state won by Kerry in 2004. McCain leads Obama by five points in Indiana and by one point in North Carolina - both states won by Bush in 2004. 6"Obama's lead is very steady. He could be looking at a big day on Tuesday," said pollster John Zogby. "These are all Republican states except Pennsylvania, and that does not look like it's going to turn for him." In Florida, the biggest prize being fought over on Tuesday with 27 electoral votes, Obama leads McCain by 48 per cent to 46 per cent. The two were running dead even at 47 percent one week ago. In Ohio, the state that decided the 2004 election with a narrow win for Bush, Obama has opened a six-point edge. He also has a six-point lead on McCain in Virginia and an 8-point advantage in fast-growing Nevada. Obama leads McCain by a statistically insignificant one point, 47 per cent to 46 per cent, in Missouri. McCain has the same one-point edge in traditionally Republican North Carolina. McCain has a solid five-point lead in Indiana, which has not supported a Democrat for president since 1964. In the national poll, Obama leads by 15 points among independents and by 13 points among women, two crucial voting blocs in Tuesday's election. He leads by one point among men and among all age groups except those between the ages of 55 and 69, who favour McCain by one point. McCain leads among whites by 13 percentage points but is only attracting about 25 per cent of Hispanics. In 2004, Bush won more than 40 per cent of Hispanics. Both independent Ralph Nader and Libertarian Bob Barr were at one per cent in the survey, with about two per cent of voters still undecided. The rolling tracking poll, taken Thursday through Saturday, surveyed 1,205 likely voters in the presidential election. In a tracking poll, the most recent day's results are added, while the oldest day's results are dropped to monitor changing momentum. White House front-runner Barack Obama duelled with John McCain on the penultimate day of the epic 2008 campaign, presenting a tableau of his loving family and vowing to change America. On the home stretch before Tuesday's election, the Democrat bidding to be America's first black president appeared before 80,000 supporters in Cleveland, Ohio with his wife Michelle and their two daughters aged seven and 10. McCain fought for a comeback win in Pennsylvania - which went Democratic in 2004 and which he must take to stand a chance of victory - as the state Republican Party ran an ad about Obama's fiery former pastor Jeremiah Wright. The Democrat's campaign has not made the age difference an explicit issue of the election, but the contrast was implicit as his young family rejoined him on the campaign trail at rallies in western states Sunday and in Ohio. At three rallies in Ohio ending late in Cincinnati, Obama again hammered McCain on the stricken US economy, and said his policies would extend President George W Bush's economic and foreign policy legacy. The presidential campaign has narrowed down to states that have been reliably Republican in recent elections, or in the case of Virginia, Indiana and North Carolina, that have not voted for a Democratic hopeful in decades. Both the candidates were to end the long day in Florida ahead of events there Monday, the campaign's final day, as each bids to lock down the state that so controversially decided the 2000 election in Bush's favour.