Here’s everything you need to know about how the process works — and how to watch the results like a pro:

How It Works

When the candidate-preference portion of the caucus begins, attendees are asked to move around the room for the “first alignment.” They walk to a designated area of the room for their favored candidate, who are represented by “precinct captains.” Then organizers tally the number of people for each candidate. There’s also a section for “uncommitted” — people who choose not to pick a candidate.

Then comes the cut. In the vast majority of districts — all but those small precincts that have a tiny number of delegates up for grabs — the viability threshold is 15 percent. Any candidate above 15 percent is deemed viable, and their supporters are locked in. (That also applies to “uncommitted,” by the way. Caucus-goers who want to see the first alignment goes before picking their candidate may need to strategically line up with a non-viable campaign in order to remain eligible to switch.)

For voters who have picked a candidate who doesn’t meet the threshold, they can either switch to a viable candidate or hope to recruit enough people to make their candidate viable. That might be possible if they are between 10 percent and 15 percent, but it’s unlikely if they are significantly lower.

After all the switching comes a second count, known as the “final alignment.” Each candidates’ supporters are tallied, and any candidate at 15 percent or above is eligible to earn delegates to the state convention later this year. The number of delegates at stake is fixed going into the caucus — it’s based roughly on the performance of recent Democratic candidates in the precinct — and the chairperson uses the final alignment count to calculate the equivalent number of delegates each candidate has won from that precinct.

The Vote (and Delegate) Count

In past caucuses, the state delegate equivalents were the only numbers provided to the public. But after a near-photo finish between Hillary Clinton and Bernie Sanders in 2016, reforms were adopted aimed at increasing transparency. Now, the state Democratic Party will be releasing all three metrics: the raw votes from the first and final alignments, and the state delegate equivalents.

If you’re watching television at home or following the returns on websites like POLITICO, you’ll see a winner proclaimed based on the traditional metric: state delegate equivalents. That includes The Associated Press, the news service of record for elections for most observers.

“Ultimately, we think that the state delegate equivalents are the most directly tied to the way that the Democrats pick their nominee,” Julie Pace, the AP’s Washington bureau chief, told POLITICO in an interview last month.

But already some candidates are signaling instead that they’ll highlight the first alignment raw vote, since it’s likely to be most favorable for them. That includes lower-polling candidates like Tom Steyer, who is in the low-single-digits in the polls and unlikely to be viable in most caucus precincts.

But it also includes Sanders, the nominal frontrunner. His campaign said it is hoping to win all three metrics, but Sanders senior adviser Jeff Weaver told POLITICO last week he sees the first alignment as “most analogous to what you’d get in a primary state.”

Once the Caucuses Begin

In order to participate, caucus-goers must be checked in, or in line, at 7 p.m. Central. It’s expected to take roughly a half hour before the first results start streaming in from the state Democratic Party, usually from the smaller precincts, where the counting and realignment processes don’t take as much time.

We will get some data right at 8 p.m. Eastern/7 p.m. Central, however: the first numbers from the entrance poll, conducted on behalf of a consortium of TV news networks.

Unlike exit polls, which are conducted after people leave the voting booth, entrance polls interview voters on their way into the caucuses. So while they can measure a voter’s intention, they do not necessarily predict what will happen during the caucus process.

Places to Watch

Iowa has 99 counties, many of them rural and sparsely populated. But here are some counties to watch once the state Democratic Party begins to report results.

Polk County: Iowa’s most populous county includes Des Moines and its immediate suburbs, areas populated by residents of a young, vibrant city and well-heeled suburbanites. It was a battleground in 2016: Clinton won it narrowly over Sanders.

The college counties: Sanders won both Johnson (Iowa City) and Story (Ames) counties by roughly 20 points in 2016, based on robust support on the campuses at the University of Iowa and Iowa State, respectively. Polls show Sanders is still the top choice among younger voters, and he’ll need to run up big margins in these areas again.

Obama-Trump country: The 2016 general election saw Iowa swing wildly toward the GOP, which flipped 31 counties Barack Obama had won in 2012. Most are in Eastern Iowa. And while the largest counties stayed Democratic — Linn (Cedar Rapids) and Scott (Bettendorf/Davenport) — counties like Clinton, Des Moines and Muscatine all went for Donald Trump. Sanders carried all five of these counties in the 2016 caucuses, but candidates traveling through there all highlighted their electability over the past few weeks.

Western Iowa: With the three senators sidelined from the trail in recent weeks by the impeachment trial, Joe Biden and Pete Buttigieg have had their run of the state among top-tier candidates. As a result, they’ve spent more time in harder-to-reach Western Iowa, which is less populated but could be a swing area in the delegate count. The two largest counties there are Pottawattamie (Council Bluffs) and Woodbury (Sioux City), but watch the county-by-county results across all of Western Iowa, from Des Moines west to the Missouri River.