First Treasury undermined Abbott's claim that his surplus was a lot bigger than Labor's. Then the new independent from Tasmania, Andrew Wilkie, punctured Abbott's boast the Coalition would never wastefully splash money around by revealing it had offered him $1 billion for the Royal Hobart Hospital, which he had rejected on the basis that it appeared to be pork barrelling.

An MP who does not like pork - how could the Coalition have picked that?

The irony is Abbott's costings would be looking more than respectable if he had not been so desperate to back up his debt-and-deficit attack with the claim that he could deliver a budget bottom line a massive $11 billion better than Labor's.

By Treasury's reckoning, the Opposition Leader's budget bottom line is still $900 million better over the next four years. If he can find savings to make up for another $3.6 million he spent from the three big infrastructure funds, then he could wind up $4.5 billion ahead. That's no mean feat since both sides first had to find savings to pay for all their election promises.

It would have been quite sufficient for Abbott to prove economic responsibility. But he did not want a tie, he wanted to win. He wanted clear differentiation. Some of the difference between the Coalition and the Treasury's figuring is because of different assumptions or information that, from opposition, the Coalition simply could not have known. The costing of the education tax refund and the paid parental scheme fall into that category.

But some is due to assertions that never looked credible and, according to the Treasury, are not.

The lazy $1 billion claimed because the Coalition says it knows better than the pharmaceuticals industry, chemists and the government how much can be saved from a deal on medicines was never going to fly; nor was the $2.5 billion from changing the ''conservative bias allowance''.