Attention, Oscar voters: Final balloting runs Feb. 6-17, and there are several useful things to know — especially regarding the best-picture race.

When the Academy of Motion Picture Arts & Sciences allowed five to 10 nominees, they changed voting procedures both for nominations and final voting. PricewaterhouseCoopers’ Rick Rosas describes the final balloting for best-pic as “an instant runoff election.”

How will your votes be counted? And why are there eight films this year, as opposed to nine last year?

Here are some facts:

1. The final ballot lists all nominees alphabetically in every categories. For 23 out of 24, the voter simply checks a box. But with best picture, the voter will assign a number, 1 through 8, in order of preference. The order of ranking is all-important. PwC will count only one of your votes, but to be safe, you should rank all eight (for the reason why, see No. 4, below).

2. Everybody votes in all 24 categories. The Academy of Motion Picture Arts & Sciences has sent a package with DVDs of nominees in five categories: foreign-language, documentary feature and three short categories (live-action, animation, docu). In the past, panels chose these because contenders were too hard to find for general voters.

3. You don’t have to fill out every category. The Academy prefers that you abstain if you haven’t seen enough of the nominees or don’t feel qualified to judge the category. (For deeper looks into below-the-line work, watch Variety’s video interviews with industry pros who have insights.)

4. Voting closes at 5 p.m. PT on Feb. 17. Once that happens, the PwC team start counting. With 23 of the 24 races, the accountants simply tally who received the most votes. But with eight best-picture nominees, the Academy doesn’t want a film to win with only 12% of the vote. So PwC begins by tallying everybody’s No. 1 pick. They create eight “stacks” of ballots, one for each film. In theory, it’s possible to have a winner in the first round, but PwC’s Rosas says, “If history is any guide, we will have to do it a few times.” If there’s no clear winner in round one, the PwC folks eliminate the lowest-tallying film, take those ballots and start counting the voters’ second choice. (The goal is to ensure that every voice is heard, and supporters of the lowest-tallying film otherwise will not be able to weigh in.)

The Academy dictated that the winner needs to win by 50%-plus-one votes. With 6,024 eligible voters, that means 3,062 votes plus one (i.e., 3,063, though it may be slightly less, depending on whether everyone turned in their ballots). Is that clear? Of course not. But the point is that no film will win the top prize without a lot of support. By round two, PwC is dealing with seven films. And so on.

5. Only two people will know all the results: Brian Cullinan and Martha J. Ruiz, PwC Oscar balloting co-leaders. They are backed by a team of four to six, who contribute to the counting process, but Ruiz and Cullinan will be the only two people in the world who know the winners before the Feb. 22 opening of the envelopes.

6. Finally, voters (and the rest of the world) may be wondering: Why are there eight films nominated, as opposed to nine or 10?

A brief history: The Academy decided in 2009 to increase the number of best-picture nominations to 10. That number continued the following year. Starting with films of 2011, the Academy decided the number would vary, with a minimum of five and a maximum of 10. For the first three years (2011-13), it happened to be nine.
Spoiler alert! The following is interesting, but pretty darn mathematical/geeky.

This year, there were 323 films eligible. So the PwC folks started by creating one stack for each film nominated. If any film has at least 9.09% of the total votes, it is automatically nominated. Why that number? Because the category will have a maximum of 10 films, so PwC and the Academy set the bar at 10-films-plus-one, or 11 films, and that 9.09% is the percentage needed.

If any film has more than 9.09%, those votes are considered surplus, since the film has already made the grade; those surplus ballots are redistributed, and PwC goes to the voters’ next choice — with those votes carrying a reduced value to reflect the votes’ original allocation to a nominated film. Are you with us so far?

In this counting, PwC also eliminates from the bottom. If any film got less than 1% of the votes, it’s never going to make it, so that ballot is redistributed, with PwC going for the person’s next eligible films.

At this point, PwC looks to see which films — that have not yet made the grade — have at least 5% of the vote. They take those films, plus the previous group of films that earned 9.09%, and see how many films they’re talking about. If the total is between five and 10, bingo. If it’s lower than five or more than 10, PwC does the whole thing over — “with a goal of determining the top five or top 10, as the case may be, using the traditional preferential voting approach applicable to other Oscar categories,” according to Rosas.

Any further questions? Feel free to ask someone at the Academy, or at PwC, or ask Stephen Hawking or Alan Turing. They apparently understand it. The rest of us don’t — but we really don’t need to.