When you use the keyboard and mouse, your shoulders should be relaxed. Your upper arm and forearm should form an angle that is slightly greater than a right angle, with your wrist and hand in roughly a straight line.
Change hand positions often to avoid fatigue. Some computer users might develop discomfort in their hands, wrists, or arms after intensive work without breaks. If you begin to develop chronic pain or discomfort in your hands, wrists, or arms, consult a qualified health specialist.
Mouse or optional trackpad. Position the mouse or trackpad at the same height as the keyboard and within a comfortable reach.
Chair. An adjustable chair that provides firm, comfortable support is best. Adjust the height of the chair so your thighs are horizontal and your feet are flat on the floor. The back of the chair should support your lower back (lumbar region). Follow the manufacturer’s instructions for adjusting the backrest to fit your body properly.
Display. Arrange the display so that the top of the screen is slightly below eye level when you’re sitting at the keyboard. The best distance from your eyes to the screen is up to you, although most people seem to prefer 18 to 28 inches (45 to 70 cm).
Position the display to minimize glare and reflections from overhead lights and windows. The stand lets you set the display at the best angle for viewing, helping to reduce or eliminate glare from lighting sources you can’t move.
For more information about ergonomics, see the Apple Support article Ergonomics.