Reference Book: Star Wars Saga Edition Core Rulebook
See also: The Dark Side
Your Dark Side Score measures the extent to which you've been corrupted by The Dark Side of The Force. A 1st-level character begins play with a Dark Side Score of 0. The only way to increase one's Dark Side Score is to commit evil acts.
A character who commits an evil act increases their Dark Side Score by 1. What constitutes an evil act is discussed under Dark Side Transgressions. Regardless of how many evil acts a character commits, the maximum Dark Side Score a character can possess is equal to their Wisdom score. Thus, a character with a Wisdom score of 15 can have a maximum Dark Side Score of 15.
A character whose Dark Side Score equals their Wisdom score has fully embraced The Dark Side and is wholly evil. A hero who falls to The Dark Side becomes a GM character (unless the GM wants to allow the player to continue playing the Dark Side character as a sort of campaign anti-hero).
Dark Side Score Tracker[]
The Dark Side Score Tracker is a useful tool for tracking a hero's devotion to The Dark Side. The Dark Side Score Tracker is represented as a row of 24 numbered boxes at the bottom of your Saga Edition Character Sheet.
A character's Dark Side Score Tracker should have a number of empty boxes equal to the character's Wisdom score. Any extra boxes should be shaded in or blacked out.

Whenever a hero's Dark Side Score increases by 1, the player fills in one of the empty boxes on the character's Dark Side Score Tracker. When a character has no more empty boxes on their Dark Side Score Tracker, they are considered to be dark.
They are now effectively lost to The Dark Side and have little hope of finding redemption. Whenever a character's Wisdom score increases by 1, they gain an additional empty box on their Dark Side Score Tracker. This box remains empty until their Dark Side Score increases by 1.
A hero who still has empty boxes on their Dark Side Score Tracker may be tainted by The Dark Side, but not beyond redemption. A tainted character can rid themselves of The Dark Side's taint by Atoning.