An overall majority in favour of the Belfast Agreement is beyond doubt. The combined SDLP, Sinn Fein and Alliance vote alone in last year's general election was 48 per cent. All three parties will complain vigorously that any majority should suffice - that, after all, being the simple principle governing any future change to Northern Ireland's constitutional position.
But for the agreement to work, it needs to be firmly rooted in both communities. The Northern Ireland assembly will operate on a consensus basis, requiring a minimum 40 per cent each of the members designated unionist or nationalist.
So what constitutes a sufficient majority? Mr David Trimble will claim victory with a 70 per cent Yes vote, and will have a good stab on anything much over 65 per cent. Mr John Taylor was preparing the ground for the battle of the spin on Thursday, insisting to journalists that the Protestant/Catholic ratio in the North is 65:35 per cent. Although the opinion polls have registered no evidence of a significant republican No vote, the Trimble camp will also argue that there is no basis for the assumption that No voters are exclusively unionist.
However, Mr Trimble himself has acknowledged that a Yes vote of between 65 per cent and 69 per cent will be a matter for judgment and debate about the actual disposition of the unionist electorate. And while 70 per cent or above will give him the immediate advantage, experts agree he needs to make the magical 75 per cent to stake his claim convincingly.
The overall unionist share of last year's vote was 52 per cent. A 74:26 per cent split today would suggest a straight 50:50 unionist split. On 30 per cent or more, Mr Peter Robinson and his colleagues will be claiming a victory.
The importance of this could not be overstated. The Trimble campaign has laid bare the scale and impact of his party's divisions. A decisive Yes vote will confirm his leadership and should enable the leadership to face down leading dissenters, hoping to obstruct the agreement from within the assembly.
Mr Trimble will also hope that a clear 2:1 margin will generate an acceptance among some opponents that the people have spoken and that the democratic obligation is now to work the agreement.
But if the antis gain any significant internal advantage, they will press it, facing Mr Trimble with a nightmare scenario of anti-agreement candidates standing under his party label, committed to joining forces with the DUP/UKUP block in the assembly effectively to overturn today's result and kill the new arrangements for the government of Northern Ireland at birth.