Explaining the New Hampshire primary

It's decision day in New Hampshire, as polling booths open across the US state in the country's first primary election for the Republican presidential candidate.

Voters in the quaintly named village of Dixville Notch opened voting at just after midnight on Tuesday.

The process of choosing a challenger to Barack Obama, the US president, is a complicated one, involving two types of polls in every US state, before the Republican national convention later in the year.

Al Jazeera's Scott Heidler reports from New Hampshire.