In the words of that under-rated political scientist Bette Davis, “Fasten your seatbelts. It’s going to be a bumpy night.” Will Hillary maintain her momentum? Can Bernie pull off the electoral upset of the decade? Will Ted Cruz own Trump tomorrow morning? Or will The Donald prove that money can buy—if not love, then an awful lot of votes in Iowa? While you wait, here are a few facts about the Iowa caucuses to help make sense of the ceremony:

1) We’ll probably never know who got the most votes. That’s because what gets announced tonight are the totals for delegates to the county conventions, who in turn elect delegates to the state convention, who in turn elect a delegation to the Democratic National Convention in Philadelphia in July. The actual caucus-vote totals for each candidate are never officially recorded or reported.

2) But surely the candidate with the most votes gets the most delegates? Nope. There are 1,681 caucuses tonight. Some of them will take place in tiny towns like Prescott (pop. 257) way down in Adams County, the least populous county in the state, with just 4,900 people—and 5 precincts holding caucuses. Iowa City, with over 71,000 people, has just 24 caucus sites. Once a candidate has reached the total needed to elect a delegate, any margin over that makes no difference to the result. In 2008, the Clinton campaign’s lack of attention to this aspect of the system left her trailing both Obama and John Edwards in Iowa, and let Obama snatch victory in Nevada, another caucus state. This time around Clinton’s team have mastered caucus math—while the Sandersistas have urged student supporters in Des Moines and Iowa City to “go home to vote.”

3) If Hillary wins, does that mean Bernie is toast? Not at all. Iowa is a mostly rural, overwhelmingly white state that voted against Franklin Roosevelt and John F. Kennedy. Tonight is all about expectations. Iowa gets attention not because of its six electoral votes but because it’s an early indicator of momentum. As the odds-on favorite, Clinton is expected to win.

4) If Bernie wins, is Hillary history? No again. Although in coming from 30 points behind in November, Bernie will have massively upset expectations—and will have shown that New Hampshire, which he is expected to win on the 9th, is no fluke. A loss, or even just a close win, for Clinton in Iowa would be damaging, but far from fatal.

5) And what do they mean about “viability?” Shortly after 7 pm, when the caucuses officially kick off, supporters for each candidate will be asked to publicly identify themselves. Any candidate who doesn’t get at least 15 percent of the voters in attendance in a given caucus is ruled “not viable,” freeing his or her supporters to be courted, publicly, by the other candidates. Which is when the fun begins. But that’s only for Democrats. Republicans don’t bother with “viability.” And the GOP caucuses use a secret ballot: You show up, write down your candidate’s name, and go home.

6) At least all these rules make it impossible for Democrats to rig the results. Not really. Jeff Cox, a former county chairman who’s supporting Sanders, told me, “The whole caucus system is subject to manipulation by the party leadership. In 1988, Paul Simon actually won the most delegates. The county chairman, a Gephardt man, held off reporting the Johnson county total until after the New York Times deadline.” MSNBC reported that this time around the Sanders camp, worried about Microsoft’s role in tallying the count, has developed its own app to allow it to double-check the results.

7) So if it’s close, it may also get messy. If you’re watching at home, keep an eye on Johnson county (home to the University of Iowa, it’s a Sanders stronghold) and Polk county (Des Moines), which are both likely to report late. You might also want to see who’s winning in the rural western part of the state. That’s a heavily Republican region, so any Democratic trend there will be an indication of who had the better field operation. If Bernie wins big in the cities, and Hillary spreads out effectively enough to take home the most delegates, we could be up long after the Republicans have gone to bed.

8) Speaking of Republicans… Glad you asked. In normal circumstances the predominance of evangelicals and Tea Partiers in the Iowa GOP should favor Ted Cruz. And everybody—well, The New York Timessaid Trump would never get it together to build the kind of ground game needed to get people to come out and caucus. We’ll find out tonight if celebrity and money trump faith and ideology.

9) Now you’ve really put me off. Anything else? You might spare a thought for the battle for third place. That’s where the real action will be on the Republican side. If Rubio comes third, the pressure on Bush to bow out will become tremendous. If he doesn’t, the clown car is likely to stay awfully crowded through Super Tuesday.