Normally, if you look at or read something on the computer monitor, you aim your eyes directly at the surface of the monitor.
With the parallel method the lines of sight of your eyes move outward toward parallel and meet in the distance at a point well behind and beyond the image. That's why it's called parallel viewing. When you parallel-view, the muscles inside your eye that control the focusing lens relax and lengthen.
Another method for 3D viewing is called cross-viewing or the cross-eyed method. You aim your eyes so that the lines of sight of your eyes cross in front of the image. When you cross-view, the muscles inside your eye that control the focusing lens contract strongly and shorten.
