HCA Question : Angles vs. Percentages

[Cube]

I have been surfing Pricescope for about a month now and I would like to start off by saying this site and forum have been very helpful.

I am looking at a diamond online with the following info and have a question about the HCA results.

(this is from the Sarin report)
Diameter 6.63
Total Depth 4.02mm, 60.7%
Pavilion Depth 2.85mm, 43.1%
Pavilion Angle 40.8 (40.7 - 40.9)
Crown Height 1.02mm, 15.4%
Crown Angle 34.8 (34.5-35.2)
Table Size 3.68, 55.6%
Culet 0.4%
Girdle 1.1% - 1.5% (1.4% average)
Proportion Grade 0

Whenever I run HCA on this diamond using the Crown and Pavilion angles I get a result of 1.3 EX, EX, EX, VG, but when I run it using the Crown and Pavilion percentages I get 1.7 EX, VG, VG, VG.

Why is there a difference between using the angles and percentages on this diamond?

I have run the HCA on other diamonds using the angles vs. percentages and the HCA results are the same. Am I missing something??

Thanks for your help, Cube.

 

[Regular Guy]

Cube,

Click on the link in the cut adviser, HCA utility, and you can read this:

"It is best to input crown and pavilion angles into HCA to reject less beautiful diamonds. We use trigonometry to calculate the angles from % data. Use angles if you have them because:
%''s are often rounded i.e. 13.3% crown height becomes 13% or 13.5%.
Pavilion depth % when converted to pavilion angle often understates the pavilion angle by 0.15°
Scanners are not good at measuring culets; a culet reduces the pavilion depth % but does not change the pavilion angle.
Sarin scanner data is better than Ogi because they calculate the angles and then scale of the %''s. Ogi works the other way round.
If you only have access to % info (e.g. EGL, IGI or HRD report) then use the %''s to reject known duds, then and ask the supplier to run Sarin angle data on your short list.

If the supplier has idealscope photos or GemAdviser files of the diamond, then they are more useful than HCA. "

 

[JohnQuixote]

Use the angles whenever possible. It''s a more accurate prediction.

 

[Cube]

Thanks for the help Regular Guy and JohnQuixote.
-Cube