Posture at your computer People who use PCs complain mostly about the following: eye-strain, specific pain in the wrists, back, neck and knee joints, general tiredness and poor concentration.
Whether your home PC is squeezed into a cubby hole under the stairs, balanced on your knees (this should only be attempted if you use a laptop) or balanced on one of those peculiar workstation/table things, there are specific steps you can take to make yourself more comfortable.
• Support, support, support. A good chair will look after the base of your spine (at first it'll feel as though it's pushing forwards slightly) and support the backs of your thighs, which should be parallel with the floor.
Sit back in the chair instead of hunching forwards and adjust the height, so that your feet can rest flat on the floor. If that's not possible, try a foot-stool or a cushion.
• Open angles. People who study ergonomics (the science of making people comfortable in their environment) believe that instead of everything being at right angles, you should try to 'open' your knees, elbows and hips to an angle greater than 90 degrees when you're at the PC.
This places less strain on the joints and increases the circulation. For the same reason you shouldn't sit with the backs of your knees flush to the front edge of the chair.
• Flat, flat, flat. Your keyboard should be parallel to your arms and if you're experiencing difficulties, try folding down the little legs at the back or adding a wrist rest for support. Keyboard trays that slide out are fine so long as they're the correct height - cheaper ones tend to be too low and you may find they make the rest of the desk too high for comfortable writing or other jobs.
Mice should be close to the keyboard so you're not always reaching for them.
• What are you looking at? Your monitor should be in front of you rather than off to one side.
Your eyeline should be level with the top edge if it's a 15 or 17" display, or a couple of inches down if it's larger.
Sit at arm's length away from smaller monitors and slightly further from bigger ones. LCD monitors are easier to position (and much easier to move) and don't flicker, which reduces the chances of getting a headache.
Diffuse lighting is better than spot-lighting. Try to have the monitor facing away from windows and other natural light sources too.
If you can't be doing with all this, at least move your position slightly every few minutes, take a moment to re-focus your eyes on something else further away before returning to the monitor and take short, regular breaks.