Applicable to:

• Brilliant
• Rounded Fancies / Marquise, Oval, Pear

There are several ways from different systems and tools to measure lower girdle facets.

Helium software supports measurement of the heights' ratio on projection to vertical plane (depth girdle facets) and measurement of the lengths' ratio on projection to horizontal plane (length girdle facets). These parameters are measured for each lower girdle facet. All measurements are made using virtual cut that does not have "Extra" facets and culet (figure 1).

Figure 1.
Helium create virtual model without "Extra" facets and culet for measurements of the parameters.

During the measurement of these parameters the three points on the cut are taken into consideration (figure 2).

First (A) point is the virtual pin of the pavilion. The culet facet is discarded and the A point is the lowest vertex, which would have the pavilion without culet. Thus the culet does not affect the parameter.

The second (B) point is the lowest vertex of the analyzed lower girdle facet. Please note that these points on the adjacent facets may not coincide on the non-ideal cut (B₁, B₂). The values of the parameters are calculated for B₁ and B₂ separately. Thus the values may differ for adjacent facets.

The third point (C) is the highest point that lies on the edge between adjacent lower girdle facets.

Figure 2.
The three points on the cut are taken into consideration. A, B₁, C for blue lower girdle facet. A, B₂, C for yellow lower girdle facet.

The depth girdle facet 1 (for blue lower facet) is the ratio between B₁C height and AC height (figure 3). The depth girdle facet 2 (for yellow lower facet) is the ratio between B₂C height and AC height.

The length girdle facet 1 (for blue lower facet) is the ratio between distances B₁C and AC, where the distances are measured in the horizontal projection (figure 3). The length girdle facet 2 (for yellow lower facet) is the ratio between distances B₂C and AC.

Figure 3.
The measurements depth and length girdle facets for blue lower girdle facet.

Depth girdle facet 1 = H1_lower / H_pavilion

Length girdle facet 1 = L1_lower / L_pavilion

Measurements of lower girdle facets are used in different systems and tools.

Comprehensive list of the Helium report parameters:

• Position normalization
• Diameters, Width & Length
• Main diameters
• Ratio (L/W) & Girdle Ratio
• Table
• Culet
• Total height
• Crown height
• Pavilion depth
• Upper and lower girdle facets' heights
• Crown height at girdle minima
• Pavilion depth at girdle minima
• Depth and length girdle facets
• Girdle thickness
• Girdle types for cushion as red, yellow, green and blue
• Corner angle width and Corner angle length
• Facets' slope and azimuth angle
• Facets' slope and azimuth angle for rounded fancies (obsolete)
• Azimuths deviation from ideal
• MIC & Girdle to MIC
• Girdle-Table offset (by table axis),
  Girdle-Culet offset (by table axis),
  Table-Culet offset (by table axis)
• Crown painting and Pavilion painting
• Girdle type (obsolete)
• Trapezium parameters
• Extra Facet / Natural
• Twist
• Statistical values

Measurements are used in different systems and tools:

• Lower girdle facets or halves
• OctoNus spread & AGS spread