From publisher blurb:
Sneaking around can be quite difficult. You have to stay out of sight, minimize any noise you make, and remain keenly aware of anyone who might be looking for you. You also have to keep track of when to reroll your Stealth check, what things might trigger Perception checks, and the special senses of any creatures who you might encounter.
Fortunately, this is a game - and we only need to roll a bucket of dice to resolve things when it would be exciting to. It can still be useful to know if a thief has stumbled across a creature that might smell or magically sense her, but it isn’t very useful for her to roll an opposed check for each of the fifty mundane guards she passes by before that. Instead, you can use the Stealth Scale: a simple, sliding scale that makes it easy for a thief and her companions to move around stealthily, in or out of combat.
The Stealth Scale, like all Straight Path products, is short and sweet - only three and a half pages of content if printed, plus a one page quick reference sheet. However, if you're reading it on your computer, as you likely are, the desktop version is optimized for desktop viewing in gorgeous two-column landscape.