As an addition to the previous posters info: you must _definately_ know what you are doing as you have to adjust the focus while the monitor is on, otherwise it would be impossible to know wether you get a good or bad result.
Also, while fiddling around in live monitors, you should only use a non-conductive screwdriver, like one completely out of plastic to avoid damaging yourself and the monitor by accident.
/Patrik
