In case anyone else wonders, it's because of parallax. From her viewpoint it's straight on, from ours (the camera) it isn't. That's why it's important to take goni measurments straight on.
Why instruct only in flexion and extension. I am a family medicine physician and my patients always need, flexion/extension, ear to ear, clockwise/counterclockwise rotation, shrugging the shoulders, and pulling the shoulders back. Most Americans are not well hydrated and should be drinking 2 qts of water/ V8 juice.
