it is applied to 3D mesh elements: tetrahedrons, pentahedrons,
hexahedrons, etc.
-- The <b>Aspect Ratio</b> of a \b tetrahedron 3D element is calculated
-by the formula:
+- The <b>Aspect Ratio</b> of a \b tetrahedron 3D element defined by
+vertices {a,b,c,d } is calculated by the formula:
\image html formula1.png