How does the next paragraph end?

How to sit at a computer
Sit using ideal posture.
Many office and personal desk chairs have adjustable backs, seats, and even lumbar support. Since the type of chair that you use will vary, try to keep the following criteria in mind :
Your upper legs should be flat against the bottom of the chair.
Your lower legs should form a 90 degree angle at the knees. Your feet should be at a flat 90 degree angle to your lower legs.