The Goniometer is a cycling-specific tool that aids in determining optimal body positioning on a bicycle. It uses a color-coded dial to measure joint angles like knee flexion, which should ideally be between 27-37 degrees when seated. The Goniometer helps find the best saddle height and arm, trunk, and shoulder angles for comfort and efficiency. Measuring various angles with the Goniometer is a standard part of professional bicycle fitting assessments.