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The stone is positioned in the standard orientation, that is, with its table horizontal and facing downwards.

Girdle thickness is measured in 720 directions in steps of 0.5 degrees. The thickness of the girdle any given direction is measured by intersecting the vertical plane that defines the direction with the facets that constitute the girdle. HPOxygen finds the upper and lower points of the intersection between the girdle and the vertical plane. The difference between the Z coordinates of these points (along vertical axis) is the final thickness of the girdle in the given direction.

If there are extra facets on the girdle, they may be treated in two different ways

• in case if the extra facet has less than 15° deviation from the girdle (steep extra facet), the extra facet is included into the girdle for the purposes of this measurement
• more than 15° (shallow extra facet), the extra facet is not included.

Unlike Crown height or Pavilion depth measurements, no virtual model is used.

The obtained arrays of values are used to draw the involutes of the girdle surface and to determine the bezel, valley and bone girdle thicknesses. The valley, bezel and bone girdle thicknesses may be measured in at most 16, 8 and 8 points accordingly for most rounded cuts. These girdle thicknesses are measured using a virtual cut without Extra facets.

Girdle Valley

Firstly the valley girdle thicknesses are calculated. The whole girdle is separated into segments that correspond to crown upper facets and pavilion halves. These segments indicate areas on the girdle with the minimum thickness, i.e. valley girdle thickness. HPOxygen searches for the minimum of the girdle thickness within each segment and retains the azimuth of the found minimum.

Girdle Valley (symmetry)

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

Girdle Bezel

The minimal values of girdle thickness (the locations of girdle valley measurements) break the girdle into areas which contain thickness maximums (bezel and bone). HPOxygen searches for the maximum of the girdle thickness within each area and retains the azimuth of the found maximum.

For each type of girdle thickness, the average, minimum, maximum and deviation of corresponding values are calculated.

Girdle Bezel (symmetry)

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

Girdle Bone

The minimal values of girdle thickness (the locations of girdle valley measurements) break the girdle into areas which contain thickness maximums (bezel and bone). HPOxygen searches for the maximum of the girdle thickness within each area and retains the azimuth of the found maximum.

For each type of girdle thickness, the average, minimum, maximum and deviation of corresponding values are calculated.

Girdle Bone (symmetry)

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