Editing Body relative direction (section)

==Traditions and conventions==
Since definitions of left and right based on the geometry of the natural environment are unwieldy, in practice, the meaning of relative direction words is conveyed through [[tradition]], [[acculturation]], [[education]], and direct reference. One common definition of up and down uses the [[gravity of Earth]] as a frame of reference. Since there is a very noticeable force of gravity acting between the Earth and any other nearby object, down is defined as that direction consistent with the local [[gravitational field]] [[unit vector]], in other words, the direction which an object moves in reference to the Earth when the object is allowed to [[free-fall|fall freely]]. Up is then defined as the opposite direction of down. Another common definition uses a human body, standing upright, as a frame of reference. In that case, up is defined as the direction from feet to head, perpendicular to the surface of the Earth. In most cases, up is a directionally oriented position generally opposite to that of the pull of gravity.

[[File:Orestes (1848).jpg|thumb|left|upright|This statue holds a sword in its [[proper right]] hand]]
In situations where a common frame of reference is needed, it is most common to use an egocentric view. A simple example is road signage. Another example is [[Blocking (stage)|stage blocking]], where "stage left" "stage right" are, by convention, defined from the point of view of actors facing the audience. "Upstage" and "downstage" do not follow gravity but by convention mean away from and towards the audience. An example of a non-egocentric view is [[page layout]], where the relative terms "upper half" "left margin," etc. are defined in terms of the observer but employed in reverse for a [[Compositor (typesetting)|type compositor]], returning to an egocentric view. In medicine and science, where precise definitions are crucial, relative directions (left and right) are the sides of the organism, not those of the observer. The same is true in heraldry, where left and right in a [[coat of arms]] is treated as if the shield were being held by the armiger. To avoid confusion, Latin terminology is employed: ''dexter'' and ''sinister'' for right and left. [[Proper right and proper left]] are terms mainly used to describe artistic images, and overcome the potential confusion that a figure's "own" right or "proper right" hand is on the left hand as the viewer sees it from the front.

Forward and backward may be defined by referring to an object's or organism's [[Motion (physics)|motion]]. Forward is defined as the direction in which the object is moving. Backward is then defined as the opposite direction to forward. Alternatively, 'forward' may be the direction pointed by the observer's [[nose]], defining 'backward' as the direction from the nose to the [[parietal bone|sagittal border]] in the observer's [[skull]]. With respect to a ship 'forward' would indicate the relative position of any object lying in the direction the ship is pointing. For symmetrical objects, it is also necessary to define forward and backward in terms of expected direction. Many mass transit trains are built symmetrically with paired control booths, and definitions of forward, backward, left, and right are temporary.

Given significant distance from the [[Geomagnetic pole|magnetic poles]], one can figure which hand is which using a [[magnetic compass]] and the [[sun]]. Facing the sun, before noon, the north pointer of the compass points to the "left" hand. After noon, it points to the "right".