Apple iMac (Early 2009) - Manual (Page 63)

Chapter 5 Last, but Not Least 63
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.
You might have to raise your chair so that your forearms and hands are at the proper
angle to the keyboard. If this makes it impossible to rest your feet flat on the floor, use
a footrest with adjustable height and tilt to make up for any gap between the floor and
your feet. Or you can lower the desktop to eliminate the need for a footrest. Another
option is to use a desk with a keyboard tray that’s lower than the regular work surface.
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).