Official recounts are underway in close ridings. Here's how they work

One vote turned out to be the difference-maker in the Montreal-area riding of Terrebonne.

The riding underwent a lengthy process where the seat flipped between the Liberals and Bloc Québécois before the official recount results were announced over the weekend.

On election night, the unofficial results showed that Liberal Tatiana Auguste had unseated Bloc incumbent Nathalie Sinclair-Desgagné. The riding was later declared for Sinclair-Desgagné but then an official recount before a judge showed that Auguste had won by a single vote.

While the back and forth may seem confusing, Laura Stephenson, chair of the political science department at Western University, says it shows a "deliberate and careful" accountability process at work.

"It's detailed, it's rigorous, it's careful. All of those things should tell you how seriously our rules and Elections Canada are taking the outcome of our elections," she said.

Three other recounts are taking place. A recount in Terra Nova-The Peninsulas in Newfoundland and Labrador began Monday, another in Ontario's Milton East-Halton Hills South will start Tuesday. Windsor-Tecumseh-Lakeshore's recount will start on May 20.

Here is how the judicial recount process works.

Election workers count every ballot by hand in front of witnesses — typically representatives of the competing candidates. They then report those numbers to Elections Canada's headquarters, which are the unofficial results that voters see on election night.

In the days following, returning officers — Elections Canada employees who are responsible for an electoral district — go through a validation process to ensure that the numbers reported on election night are accurate. That validation process is different from an official recount.

"When you're talking about hundreds of or thousands of polling locations and lots of results coming in, errors can happen. Whether it's something gets misheard on the phone or somebody accidentally types in the wrong number on the keyboard," Matthew McKenna, a spokesperson for Elections Canada, told CBC News before election day.

"The returning officer for each riding goes through the statements of the vote from every poll and makes sure that that's checked against the records so that we can adjust for any little errors or mistakes."

Unlike official recounts, the validation process happens in every riding. When results are extremely tight after the validation process, recounts are triggered.

A judicial recount will automatically be triggered if the number of votes separating the winner and a runner-up is less than 0.1 per cent of the total votes cast.

This was the case in Terrebonne, Terra Nova-The Peninsulas and Milton East-Halton Hills South.