GSS. With a sit-stand desk, stand upright with your legs apart and slightly bent with one foot marginally in front of the other. Your elbows should be level with the desk. It may be necessary to raise or tilt the monitor slightly to align it in the way described in G3 in order to avoid tipping your head forward. Be sure to mix sitting and standing. 5 to 6 minutes of standing for 30 minutes sitting is recommended.
BSS. It is too easy to just replace a static sitting posture with a static standing posture! Many users set the desk too low for standing height. As a result, they slouch forward and then tilt their head up (especially those using varifocal spectacles). This creates the classic (and very uncomfortable) ‘vulture neck’. Many people also lock their knees which restricts blood flow.