Grading the symmetry of round brilliant cut diamonds in Russia

In Russia, there are certain specifications used both to cut diamonds and to grade them. These specs have been developed at «Kristall» factory (Smolensk) and are referred to as TU 117-4.2099-2002 (Diamonds, 2002). According to these specs, the cut quality of a round brilliant cut diamond can be graded as «A», «B», «V», or «G» (the «°» grade is the best). A stone whose cut quality does not fit even the «G» level is considered as not compliant with the specifications. The specs contain the tolerances for cut parameters of «°»- and «B»-graded diamonds and the requirements whose violation should be treated as asymmetry. For the «°» group, the allowable error in the girdle roundness is 0.06 mm for stones with a diameter less than 3.00 mm, 2% of the diameter for stones with a diameter from 3.00 to 5.00 mm, and 0.10 mm for stones with a diameter exceeding 5.00 mm. For the «B» group, this error is 0.08 mm for stones with a diameter less than 3.00 mm, 2.5% of the diameter for stones with a diameter from 3.00 to 5.00 mm, and 0.13 mm for stones with a diameter exceeding 5.00 mm. For the «°» group, the displacements of the culet and table center with respect to the diamond axis must not exceed: 2% of the stone diameter for a diamond with a weight less than 0.30 ct, 1.5% of the stone diameter for a diamond with a weight from 0.30 to 0.99 ct, and 0.5% of the stone diameter for a diamond with a weight exceeding 1 ct. For both groups «A» and «B», the allowable irregularity of the girdle thickness (the difference between the maximum and minimum values of its local thickness) is 25%, and for those diamonds heavier than 1 ct the girdle must be visually uniform along the whole perimeter. The upper facets should be above the lower ones. For diamonds whose weight is less than 1 ct, the allowable displacement of upper edges and nodes with respect to lower ones is: 10% of the base of an upper girdle facet or crown facet for the «A» group and 20% of that figure for the «B» group. When an «A»- or «B»-graded diamond whose weight exceeds 1 ct is viewed through a 10x loupe, all its upper cut elements must be visually symmetrical to the corresponding lower cut elements. The difference in the tilt angles of both upper and lower facets with respect to the girdle plane, measured for a single diamond, cannot exceed: 1° for the «A» group, 2° for «B», 3° for «V», and 3° for «G». There are also some requirements for additional facets.
After a diamond is cut, it is passed to the quality control department, members of which, guided by the specifications, may claim: non-roundness (code 06), over- or undercut (code 11), top-to-bottom displacement (code 16), table displacement (code 17), girdle displacement (code 19), crooked girdle (code 23), and some more flaws.