central distance
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central distance. The central distance for a face or form (set of symmetry-equivalent faces) is the perpendicular distance in arbitrary unit of the user's choice (often referred to as central distance units) from the center of the crystal coordinates to the face in question. Generally, the larger the central distance the less prominent (smaller) the face is.

SHAPE uses finite tolerances in many parts of the calculations, for example to test whether corners formed by the intersection of three faces are coincident with existing corners, whether faces are parallel, etc. Usually these tests work best when the central distances are approximately 1.0 or smaller. However, if the results are obviously incorrect, changing all the central distances by a factor of 10 up or down with the Factor button in the Forms List Dialog may improve things.