GIA Facetware vs HCA?

[stanelz84]

Hi All! Not sure if anyone has discussed this before on the forum, but am hoping to find out what the main difference is between the two calculators. What if one doesn't "match" with the other like this center stone: Any help is appreciated!

1.71ct G Si1 $14900
7.72 - 7.74 x 4.71 mm​

Cut Excellent​

Polish Excellent​

Symmetry Excellent​

None Fluorescence​

HCA 2.9​

Light Return Very Good​

Fire Very Good​

Scintillation Very Good​

Spread for weight Very Good​

GIA Facetware​

Crown Height*16.6%
Pavilion Depth*42.6%
Total Depth*62.8%
Estimated Grade EX​

Proportions
Depth
60.9 %
Table
59 %
Crown Angle
33.5°
Crown Height
14.0%
Pavilion Angle
41.2°
Pavilion Depth
43.5%
Star Length
50%
Lower Half
80%
Girdle
Medium, Faceted, 3.5%
Culet
None

 

[stanelz84]

Any help is appreciated. Thank You!

 

[Texas Leaguer]

Both are similar tools, though independently designed. Therefore you will see some differences in the results. Different assumptions or opinions of what looks best are reflected in the outputs. The GIA model (Facetware) is the foundation of the GIA cut grading system and based upon ray tracing research and validated by a long term study consiting of some 70,000 of observations. However, many people believe that it is too broad and forgiving. HCA tool is stricter in certain areas and as such is a good tool for weeding out some of the outliers in the GIA Ex range.

It is important to understand that both tools are table-based. That is, the limited inputs correlate to outputs/grades that are predefined. Since the inputs are rounded and averaged and do not take into account all of the facets, neither can tell you how a particular stone performs. It can only give you some probabilities. The GIA tool will however tell you how a given diamond will likely grade on their cut grade system.

The AGS light performance system is diamond-specific. The output is based upon ray tracing a 3D model of the actual diamond taking into consideration the contribution of all of the diamond's facets.