TORONTO -- Political parties have a new tool to assure voters that their pricey promises won’t cost more than their advertised sticker price, but one week into the campaign, some of them seem more eager to use it than others.

This is the first federal election in which parties have been able to submit their proposals to the Parliamentary Budget Officer (PBO) for non-partisan costing.

While parties have traditionally provided fully costed versions of their platforms during election campaigns, they have had to find their own outside experts to cost them. One party could have used a friendly think-tank for its projections while another could have relied on a former high-ranking Department of Finance official – theoretically allowing for differences in accounting style that could make apples-to-apples comparisons between parties difficult.

Having the PBO involved means the same team will be going through the promises of all parties who request their expertise. Parliamentary Budget Officer Yves Giroux has said this will lead to greater transparency and, ultimately, greater trust in political parties.

“There’s a lot of gravitas behind the PBO numbers,” former parliamentary budget officer Kevin Page told CTVNews.ca Tuesday via telephone.

Discussions about expanding the PBO’s mandate to cover election promises began during Page’s term as the PBO, which ended in 2013, but didn’t come to fruition until the 2017 budget.

The PBO will not cost an entire platform at once, but parties could achieve this effect by asking the office to cost each individual proposal and tally up the results.

“PBO doesn’t provide the roll-ups of all the individual party proposals. They just cost the individual measures,” Page said.

“When (Conservative Leader Andrew) Scheer says he’s going to balance the books in the next five years or (Green Leader) Elizabeth May says she’s going to try to balance the books over the next five years, we haven’t seen those plans – and PBO doesn’t do that work.”

In the run-up to the campaign, some parties seemed keener than others to make use of the PBO. The Liberals, NDP and Green Party all said they would have the PBO cost their platforms, while the Conservatives appeared more hesitant before they eventually agreed to do the same.

Since the campaign began, however, it is the Conservatives who seem to have been making the most liberal use of the PBO. They’re responsible for six of the eight costings the office had publicly released as of Tuesday afternoon.

“Andrew Scheer and Canada’s Conservatives will be using the Parliamentary Budget Officer to cost every platform commitment that has dollars and cents attached to it,” Conservative spokesperson Simon Jeffries told CTVNews.ca in an email.

The Conservatives’ consistent use of the PBO has earned a fan in Page – something he sees as ironic, given the constant sparring between him and the party when he and they were in office.

“I really like the way they’re rolling it out,” he said.

The other two published costings relate to NDP promises made before the campaign began. Party spokesperson Melanie Richer told CTVNews.ca via email that the NDP is “working with the PBO on costing many of our commitments and will be releasing more details throughout the length of the campaign.” She said she was unable to provide an exact number of proposals that would be costed through the PBO.

Liberal Leader Justin Trudeau was asked about his party’s lack of publicly-released PBO costings at a campaign stop in St. John’s, N.L. on Tuesday. He responded by saying that the Liberals would use PBO estimates for “a number of our platform announcements” and that PBO engagement will be “abundantly” clear when the party releases its platform.

“We will have a full costing of the Liberal platform with all the great work done by the Parliamentary Budget Officer in due course,” he said.

The Greens released their platform Tuesday without the promised PBO costing. Party spokesperson Rosie Emery said via email that PBO costing would be released “shortly” but did not have an exact date. The party’s platform includes making it mandatory for all parties to submit all their policy proposals to the PBO for costing.

Page said he would be surprised if the Greens’ platform could be fully costed in a matter of days, noting the sheer volume of proposals it contains.

In an interview Monday on CTV’s Power Play, Giroux confirmed that the Conservatives, NDP and Greens have all asked him to cost at least some of their promises. He did not mention the Liberals, but stressed that this was because legislation requires him to keep any requests confidential until they are disclosed by the parties themselves.

“Until a party publicly releases that, I’m bound by confidentiality rules,” he said.

The PBO has also created a ‘Ready Reckoner’ tool that allows users to play around with tax rates and credits and see the outcomes for themselves.