Many people have learned to shoot by closing one eye, while sighting or aiming the weapon with the other.
In recent years, however, this somewhat-traditional method of sighting or aiming has been revisited, particularly among hunters. An article by Dean Phillips, entitled "Eyes of a Champion", published in the June, 1990 issue of Bowhunting World reviews the question of shooting with monocular vision (i.e., with one eye closed), as opposed to the advantages of shooting with binocular vision (i.e., with both eyes open). This article asserts that one eye may be dominant over the other. The article further counsels that with moving targets, or in low-light conditions, there are distinct advantages to shooting with both eyes open.
For those who have learned to shoot with one eye closed, the problem of relearning binocular vision is somewhat difficult. Being a creature of habit, a person who has learned to shot with one eye closed may experience some difficulty in relearning how to shoot in order to have the advantages of binocular vision.
Accordingly, it would be generally desirable to provide a device which may be readily attached to a bow or firearm, and which will facilitate a person's transition from monocular to binocular vision while shooting. At the same time, it would be desirable to provide a device to facilitate shooting with binocular vision for those persons who have learned this skill.