This lecture covers the importance of calibration in gait kinematics, explaining how the anatomical frame differs from the technical frame and the process of anatomical calibration. It also discusses the use of optical systems and inertial sensors for calibration, providing examples of knee joint calibration and functional calibration. The lecture emphasizes the need for precise alignment and assumptions in calibration procedures, showcasing different methods to align frames and sensors. Additionally, it explores specific tests and movements used for functional calibration, such as defining functional movement in anatomical planes and aligning sensors using known axes.