Helium help : Comprehensive list of report parameters
Depth girdle facets and length girdle facets

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.

Real and virtual models

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.

Three points on the cut are taken into consideration

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.

Mesurements Depth girdle facet and Length girdle facet

Depth girdle facet 1 = H1lower / Hpavilion

Length girdle facet 1 = L1lower / Lpavilion

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

DiamCalc Brilliant Cut Parameters