Find the boney protrusion at the base of the back of your skull, then part the hair 2.5cm above, and 2.5cm to the left of this area. This will be the location of the O1 electrode.
As with the C3 site, abrade this skin with some abrasive gel on a cotton tip for about 30 seconds (this area is also difficult to get a clear signal from, so the longer you spend abrading the site, the better).
Follow the same process of applying the electrode as in the C3 step, repeated here:
Take the remaining electrode and stick it down firmly over the prepared skin such that a 'worm' of paste squeezes through the opening at the center of the gold-cup. The wire should run down and over the shoulder towards the headbox.
Of the hair that is parted above the electrode, take a pinch and pull it down over the electrode – using the paste from the 'worm' to stick the roots of the hair down over the top of the electrode.
Then take one of the paste-filled gauze squares and 'squish' it down over the electrode and hair.
Take the end of the electrode and plug it in to the O1 port (4th in from the front right of the headbox).