Eye Dominance Test

To test which eye is dominant,  simply hold your arm out straight in front of you and line your thumb up with some mark on a distant wall.  Then close or cover one of your eyes.  If your thumb seems to jump to one side,  you have closed the dominant eye.  If your thumb still lines up with the mark,  you are looking through your dominant eye.  For me,  this is my left eye.

left eye closed	both eyes open	right eye closed
The fact that my thumb seems to jump over when I close my left eye,  means that my left eye is the dominant eye when I have both eyes open.  This makes sense because I'm left handed.   If you are right handed,  your thumb will probably jump when you close your right eye,  though some people are right handed and left eyed,  or left handed and right eyed.

When I aim a rifle that has open sights,  I keep both eyes open.  That way the sights are transparent and seem to be superimposed on the target.  But I hold the rifle against my left shoulder,  with my left hand on the trigger,  and it is my left eye that is lining up with the target.