Excellent question! Instead of trying to re-explain it, I dug into the good ol' Snapzu functionality write-ups logbook and found this gem that should explain everything! It's dated from Oct 2012, quite a long time ago!
The global score of a snap will be collected using a best-of format from all of its sources. Each tribe, feed and other source will have it's own independent vote score, however the snap's global snap score will be generated by calculating all up votes vs all down votes from each of those sources. This global snap score will be used to rank snaps in order on the front page (from multiple tribes).
When a snap is created and submitted into up to 5 tribes (let's say; worldnews, politics, funny, interesting, and humor), it gets automatically up voted by snap owner in each tribe, hence getting a (7 up votes to 0 down votes) in the best-of 7, and getting a +1 in the global snap score, while getting a +1 in each tribe.
When another user goes to tribe "worldnews", sees this snap and up votes it, the global score of this snap goes up by another +1 (to +2) because the first up vote always wins the best-of by at least 1 vote (in this case: 1 up vote to 0 down votes). If this same user goes to another tribe and finds the snap again, it will be in un-voted neutral state (shows both arrows grey) in that tribe, and their next vote can mean 2 things:
1. If up vote, the tribe score goes up +1, the snap best-of goes up to +2 (2 up votes to 0 down votes), however the global snap score stays unchanged at +1 since it was the same user that voted it, and one user can only change the snap's global vote score by 1 point.
2. If down vote, the tribe score goes down -1, the best-of goes back to 0 (1 up vote to 1 down vote), and the global snap score goes back to neutral, this removing a point from the global score, meaning that the user's next vote for the same snap from a different source is another swing vote that will break the tie.
The best-of vote score for the entire snap (either +1, 0 or -1) for that user will never be displayed, so the user will never really know what their global vote score for that snap is (unless they remember exactly how they voted).
When counting reputation from snaps, the global vote scores (from best-ofs) will be used in the calculation as one user can only affect another user's reputation once from one snap. A user's self votes (made automatically) do not count toward their reputation.
Now... it may sound complicated but we feel that it improves on the current voting system used by that other site in the following ways:
1. Each tribe can have it's own vote score. This is important because it allows them to stay individually vote independent where no tribe can piggyback off another tribes or even the front page's votes.
2. It removes a lot of the luck element in voting. Snaps have multiple chances to succeed especially if submitted to the max allowed tribes. If you get a down vote in one tribe, you are still at the original score in the others. You would have to be down voted from all the tribes, and that usually means it's poor content.
3. Users can easily discover similar tribes because the tribes are listed in the snap, along with on the front page list.
I hope this answers your question!
Edit: The original write-up mentions an "other" source. This has basically been renamed to the "front page" source (as shown on the right of each snap, where the tribes are listed). It makes more sense for new ...
Edit: The original write-up mentions an "other" source. This has basically been renamed to the "front page" source (as shown on the right of each snap, where the tribes are listed). It makes more sense for new users, but it does include any votes that come in from other sources (such as google, etc.)
Thanks for the explanation! I'm sure it's just something I'll have to get used to.