The Angle Compass is a tool that is intended to assist a Blader in angling the tilt of a launch. A red ball will move when the Angle Compass is tilted along with the Launcher - the intention is to use the red ball as a guide.
In practice, the Angle Compass is merely a decorative cosmetic item, with inaccurate indications of tilt and non-reliability. The Takara Tomy release can be attached to any Launcher Grip, but the Hasbro release can only be attached to the Custom Grip and the Rev Up Launcher.