Fig. 1
From: Accuracy and reliability of tridimensional electromagnetic sensor system for elbow ROM measurement
Diagram of the coordinate system. Anatomical landmarks on the humerus, radius and ulna (pg; greater tubercle of humerus, pm; medial epicondyle of humerus, pl: lateral epicondyle of humerus, pr: styloid process of the radius, pu: styloid process of ulna, plm2: midpoint of pm and pl, and pru2; midpoint of pu and pr). The elbow joint flexion angle ϕ was defined as acos (uy · fy)