Introduction- Quantitative gait analysis is becoming an important clinical tool for assessing pathological patterns of locomotion. Euler angles are generally used to define the relative motion between segments at hip, knee and ankle joints. By definition, the distal segment moves through three successive finite rotations of flexion-extension, ab-adduction and axial rotation relative to the proximal segment at a particular joint (1,2). In a video motion analysis system, orientation of both proximal and distal segments are defined by embedded coordinate systems which are derived from body surface markers. The construction of the embedded coordinate system is susceptible to errors due to misalignment of markers. In this paper, we quantify the effect of these errors on the distal angles using the knee joint motion as an example.