From what we've seen so far, Nicola Sturgeon can win this election with a selfie stick

Even a televised debate on the first full day of campaigning failed to make much impression.

This will be a long campaign and, with the SNP enjoying an unassailable 34 point lead according to the latest poll, could be slow to catch fire. The main job for the parties right now is to make themselves heard, to get their key messages across. That explains the unusually polite tone of the opening exchanges.

It won't last. The BBC's first leaders' debate from Glasgow may have been a little tame but it revealed a lot about how the campaign will unfold.

It exposed bigger differences between the parties than at any previous Holyrood election and, as May 5 draws closer, they are sure to lead to sharper clashes.

The reason for that is simple. This is first election where tax has been an issue.

Holyrood's new powers, coming into force within the lifetime of the new parliament, mean MSPs will be responsible for raising half the money they spend.

It means that parties that wish to spend more (which, in the current austere climate, amounts to cutting less) face the tricky task of telling voters they'll pay more income tax. Parties that want to spend less, well, there are none of those.

Even Ruth Davidson, the Scots Tory leader, told her party - slightly apologetically - she would copy George Osborne's plans, including the pretty generous tax cut for higher rate income tax payers unveiled in the Budget.

As for the others, Nicola Sturgeon's SNP proposes much more modest tax cuts from 2017/18, when Holyrood takes (almost) full control over income tax. With the help of some rhetorical trickery it allows the First Minister to claim she will have an "additional" £1billion to spend. Additional compared with following Mr Osborne's plans, that is.

Labour and the Lib Dems would raise significant extra cash by putting up income tax by 1p. Labour would go further with the additional rate, raising it from 45p to 50p.

That, essentially, summed up a good chunk of the BBC's debate. The party leaders were also quizzed about education and welfare but, in this election, they are secondary to the tax debate. New investment in schools or more generous benefits have to be paid for, after all.

None of the leaders put in a disastrous performance at the BBC, though David Coburn, UKIP's MEP for Scotland, had his moments.

Ms Sturgeon was assured, persuasive and professional. As ever. Kezia Dugdale, the Scottish Labour leader, who is less well known by the public, will have been pleased with a strong performance.

Ruth Davidson, the Scots Tory leader, had the most reason to be disappointed. She was challenged over Mr Osborne's Budget cuts to disability benefits and Iain Duncan Smith's resignation and was caught squarely in the flak. She also failed to turn the debate towards independence, missing a chance to sell her party as the true defenders of the Union. Ms Sturgeon, who wants to park the issue until after the election, and Ms Dugdale, who also wants to avoid constitutional issues as she seeks to win back former Labour voters who backed Yes 18 months ago, will have been happy it never came up.

So that's how the election is shaping up. There is another factor, though, that is likely to trump all others. A Survation poll on the first day of the campaign produced "favourability ratings" for all the party leaders - the difference between whether people feel favourably or unfavourably towards them. Ms Sturgeon was streets ahead of her rivals with a rating of 21. All the others were in minus numbers: Greens leader Patrick Harvie on -1, followed by Ms Davidson on -6 and Ms Dugdale on -9.

The Nationalists know Ms Sturgeon - whose appeal transcends party allegiance - is their biggest asset and are set to fight the most presidential-style election Scotland has ever seen. As she tours the country over the coming weeks, the SNP leader's selfie stick will be as big an electoral weapon as her tax policy.