Rank (skill)

Overview
Each skill is given a rank equal to the amount of skill points you spent on that skill (skill points spent on cross-class skills count only as 0.5). Your final skill score is thus given by Rank + ability modifier + misc modifiers, rounded down as usual.

Mechanics that depend on Skill Rank
Most of the time, what matters is the final skill modifier. However, some mechanics check the skill rank.

Trained Skills
Trained skills can only be used if you possess at least one rank, regardless of any bonuses. If you have no ranks, your character sheet will display 'n/a' for all columns in the skills tab.

Trained skills include:
 * Disable Device
 * Open Lock
 * Tumble
 * Use Magic Device

Prerequisites
Some feats or abilities have skill ranks as a pre-requisite.
 * Most Bard songs require a minimum number of ranks of Perform.
 * Single Weapon Fighting feats require ranks of Balance.
 * Improved Bardic Music requires ranks of Perform.