Holloway Cut Adviser or HCA
With my first Ideal-Scope I observed there is an inverse relationship between Crown and Pavilion angles. If a crown angle was one degree steeper than the ideal of 34.5° then the best pavilion angle would be 0.2° less than the ideal of 40.75° (and vice-a-versa). The crown:pavilion inverse relationship is 5:1. Knowing this helped me buy better cut diamonds from the mid 1990’s on RapNet™, the very first online B2B service. As one of Martin Rapaport’s first subscribers outside USA, we have had a good relationship for decades.
In 1998 the GIA published a Brilliance article. Sadly the scientists were all geochemists (doing an optical study??) and they missed the real relevance of their research. When I showed them in 1999 the importance of the inverse relationship they fobbed me off. I sent them the image below of one of their charts with my black lines added proving they had discovered the inverse relationship between crown and pavilion.
It took GIA another 8 years before they launched a round diamond cut grading system which they copied from HCA. They still have not been able to develop cut grading systems for other diamond shapes.