Fig. 1From: Quaternions as a solution to determining the angular kinematics of human movementProducts of imaginary numbers comprising a quaternion. Given any starting point, moving in a counter-clockwise direction (with the arrows) gives the results of the products of the imaginary numbers (e.g., k.i = j). If the motion is clockwise then the product is negative (e.g., j.i = −kj)Back to article page