Blender's Inverse Kinematics (IK) constraint requires you to enter the 'Pole Angle' to align the bone chain to the pole target. This video is a demonstration of an add-on that I wrote to automatically calculate what this pole angle should be. Get the Bone Math extension from the official Blender Extensions platform here: Check out the source code here: Huge thanks to Jaroslav Jerryno Novotny for originally showing how to do this calculation: