It is said to be better to be equipped with a lie detector than a calculator if you want to predict the outcome of a political leadership contest, as those experienced in them can attest.
The 2003 National spill when Don Brash unexpectedly ousted Bill English as leader was the most notable for recriminations over who had broken whose pledge of support to the incumbent.
One certainty is that most MPs will vote according to one criterion, self-interest, or which candidate is more capable of saving their bacon in the September election, incumbent Simon Bridges or challenger Todd Muller.
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The 1News Colmar Brunton poll should not make Friday's decision any easier for the National caucus given that it is almost the same result as Monday's Newshub Reid Research, 29 per cent in Colmar Brunton to 30.6 per cent in Reid's.
But it almost certainly will.
The psychological effect of slumping from the 40s into the 20s may swing a few votes in Muller's favor. Although that does not mean he will necessarily win.
What might save Simon Bridges is the backing of Judith Collins.
She does not have enough support to be a contender herself, but she has the satisfaction of knowing that she has enough supporters to influence the outcome.
Collins is also one of only two or three of the caucus who experienced the devastation of 2002 on National.
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It is very difficult to recover from the 20s as English knows, and Andrew Little knows from 2017 when he stood aside at about 25 per cent and free-falling.
Jacinda Ardern was the circuit-breaker but Todd Muller is no Jacinda Ardern.
Simon Bridges did not surmount the challenges under the Covid-19 crisis and the adulation heaped on Ardern but he had withstood the pressures of leadership until then.
People may find Bridges so unlikeable that he cannot sell National's message.
But Muller is completely untested in high-pressure politics and could falter as the highly likeable David Shearer did under the high expectations set by his caucus.
One of the questions the caucus may be asking is which of them will inflict the least damage on the party.
A close result in favour of Muller will leave an unhappy and potentially destabilising rump of Bridges supporters.
A close result in favour of Bridges will undermine his leadership credentials up to the election.
The contest itself may be damaging enough to keep the party in the 20s. There will be risks either way.
A dice might be better than a lie detector or a calculator.