Star Length

Star Length is a relative measure describing the ratio between the size of a star facet projection in the direction normal to the table edge to the distance from table to girdle in the same direction.

To determine the Star Length, the model is projected onto the table plane. The common edge of the star facet and the table is located (AB on the picture below). The furthest point of the girdle in the direction normal to the edge is then found (C on the picture), and the distance from it to the edge is measured. The furthest point of the star facet itself in the same direction is also found (D on the picture), and the distance from it to the edge is also measured. Star Length is determined as the ratio of these two distances.

For compatibility reasons, Star Length is reported together with its complement to 100% and called Star : Upper Ratio in the reports. The two values appear in the report colon-separated, first the Star Length, then (100% - Star Length).

Star Length (symmetry)

Star Length (symmetry) is defined as the maximum difference of Star Length measurements, i.e. the same as deviation of Star Length value. As all symmetry parameters, it is an estimate of a deviation from perfect symmetry, and should be zero for an ideal stone.