The CBC decision desk is ready to make the call for election night: It’s an NDP victory.

An hour later, the scenario changes and Tony Parsons declares the Liberals have won another term in government.

mi-bc-130513-bts-clancy

CBC reporters Theresa Lalonde and Natalie Clancy prepare for Tuesday's B.C. election. (CBC/Petti Fong)

Twenty-four hours before voters head to the polls and it is rehearsal day Monday at the CBC for dozens of reporters, technicians and producers.  

Voting stations open from 8 a.m. to 8 p.m. PT Tuesday for the 40th general election in B.C. with the B.C. Liberals hoping to win their fourth term in government and the NDP wanting to regain their place in government after being relegated to opposition since 2001.

All the scenarios have been run through, from a Liberal minority to an NDP one and then the possibility of a majority for either of them. Two rehearsals Saturday, two on Monday and a fifth one just a few hours before results begin to come in shortly after the Tuesday night hockey game.

Stand-ins for the analysts and commentators who will be on air for CBC Radio, TV and CBC.ca Tuesday night pretend to express their surprise or to gloat over the results that are coming in. Control room 55 where normally four people run the news program has tripled its content with eight extra bodies.

Reporters and analysts watching laptop screens calculate the results of who is winning in each of the province’s 85 seats. The number everyone has their eye on is 43. Whichever party hits 43-elected members first forms a majority government.

At the time the legislature was dissolved on April 16, there were 45 Liberals in government, 36 NDP members and four independents. Sharon Musgrave, who will be making the call on the CBC election desk, says raw data comes in but numbers alone can’t predict the results.

"I make the call based on certain percentages of votes and who is leading in the votes and then we look at those parameters and whether the parameters make sense and whether we feel safe enough to make that call," she says.

"If it was just a numeric system, we can have a machine decide but sometimes it’s a feeling. Someone tells us they’ve seen  a lot of signs somewhere, someone says they haven’t seen this candidate at all so it’s not just a machine, but people doing analysis."

Musgrave says she looks at not just the riding by riding results but the landscape of what is happening by regions and whether there are trends emerging after the polls close.

The CBC is part of a consortium with the other networks in receiving numbers from each of the polling stations as soon as they come into the system, but each network makes the decision based on their own analysis of when to declare which party has won.

Senior producer Bob Weiers does a critique after each rehearsal noting when cues haven’t been picked up properly or scripts on the prompters aren’t up soon enough when the decision is made.

"The whole thing will go down if that person doesn’t know what script to roll on," he says during the debriefing after the Monday morning rehearsal. "That person has to be on their game."

Later, Weiers says the reason why there are so many rehearsals is to ensure that on election night, there are no surprises.

"We don’t want to foreshadow the results but we have to rehearse all the possible scenarios. There is so much co-ordination between the technicians and the producers and the reporters and deployment of so much equipment that it has to go right on that night," he says.

CBC's election coverage of the 40th general provincial election begins at 7:30 p.m., a half hour before the polls close in B.C. We will be on the air until viewers know who is the next premier of British Columbia.