Documentation unclear on how score is calculated

I've looked through the README file and the documentation in the Drupal.org handbook. After reading both, how score is calculated is clear as mud to me.

Here's how I think it works, but I'm not sure at all:

1) Each filter assigns a score to a piece of content from 1 to 99.
2) This score is then multiplied by the filter's gain. This multiplier ranges from 0 to 2.5 (250%). We'll call the result of this the filter's "weighted score."
3) The weighted scores from each filter are added together to give the content's "total score."
4) The total score is compared to the threshold. If the total score is above the threshold, it's flagged as spam.

If this is accurate, let me know and I will be happy to update all documentation. If it is not correct, please tell me where I'm wrong.

And one follow up question: How does the module arrive at the score generated in step 1 above? Is it just some totally arbitrary number?