Calgarians now have less than 72 hours to provide feedback on the city's proposed arena deal with the Calgary Flames — if they want their comments to be part of the official record — but many people remain confused about the financial figures in the tentative agreement.

The city has imposed a deadline of noon on Friday for citizens to offer their opinions by phone, fax, online form, email or traditional mail and have those comments included in the package of information presented at Monday's council meeting.

That's when members of council are due to vote on the nearly $600-million project.

After some confusing and seemingly contradictory information was made public late Monday night, however, some fundamental details about the deal remained murky as of Tuesday.

CBC News has asked the city for clarification on several questions related to the financial figures but has yet to receive a reply.

University of Calgary economist Trevor Tombe, however, helped cut through some of the confusion.

Here are the city's numbers and Tombe's explanation of what they mean.

$400M over 35 years: Is that in 2019 dollars?

Front-and-centre in the city's communications about the arena deal has been a figure of $400.3 million.

This is the projected return on the city's investment in the arena project. The money is expected to come from a variety of sources, including a ticket tax, a share of the arena's naming rights and increased property tax from new developments.

But in smaller print on the infographic the city has been circulating is a key qualifier to these revenue estimates: "over 35 years."

The city released this infographic as a primary point of its public communications on the arena deal. (City of Calgary)

Given that the term of the deal spans three and half decades, the question was raised during Monday's council meeting: Are these figures reported in current dollars? And do they account for things like inflation and the opportunity cost of what that money could otherwise be used to do?

The written city report says no, they do not.

It states that the net-positive bottom line of $109.9 million ($400.3 million less the $275 million in construction costs and $15.4 million in costs related to transactions and demolishing the old Saddledome) is reported in "nominal dollars" with "no time value of money reflected."

Financial estimates in the city's report on the proposed arena deal. (City of Calgary)

This, Tombe pointed out, could be problematic in an agreement that lasts until the mid-2050s.

"To whoever wrote the 'financial analysis' section: I'll give you $1 million in 35 years in exchange for $900,000 today," Tombe tweeted on Monday, during the council discussion.

"I'm dead serious. According to your analysis, it's $100,000 in pure profit to you!!"

But, later in the meeting, council heard — verbally — that there is a different figure, one that is not in the written report.

This figure does take into account the time value of money.

And it's not a positive number.

Negative 'net present value'

Carla Male, the city's acting chief financial officer, told councillors late on Monday night that the "net present value" — a measure commonly used to evaluate investment decisions over long periods of time — was projected to be negative.

This figure, which does factor in things like inflation and opportunity costs, is estimated at –$47 million, she said.

And this is the figure that Tombe believes is more relevant, when looking at the project in strictly financial terms.

The written report was confusing, in Tombe's view, but the verbal report was clear.

"Bottom line: these [numbers] are clearly saying that the city will not be making money from the investment," Tombe said in an interview on Tuesday.

"The whole project is equivalent to losing $47 million today."

That said, Tombe also pointed out that the negative number doesn't necessarily mean the arena is a bad deal for the city.

Non-financial and 'intangible' benefits

That's because "net present value" only evaluates an investment decision in financial terms, Tombe said, but there are other factors at play when it comes to a municipal government's decision on a project like this.

"There are non-economic considerations," he said.

This is a point Mayor Naheed Nenshi has made, as well.

"Not all public benefit is about dollars and cents," said the mayor, who supports the deal.

"Public benefit is also about those intangibles. It's about bringing community together. It's about uniting people. These things are hard to quantify, but they exist."

Tombe says the question before Calgarians over the next few days — and before council on Monday next week — is how to weigh all this, together.

"We should be asking: Is the $47-million net cost, all in, worth all the intangible benefits?"