Using the HCA

[cherij0411]

How come when I plug the nubmers in and use the pavillion and crown % it gives me excellent and .6 as a score but when I put in the crown and pavillion angles it only gives me very good and 1.9 as a score?


Thanks
Cheri

 

[yssie]

From HCA main page:

You need Total Depth %, Table % and Crown deg and Pavilion deg angles from AGS and 2006 GIA and IGI reports.Some reports list less accurate rounded Crown % and Pavilion %'s; run the stone and if it scores under 2.0, ask the vendor to get you a Helium, Sarin or Ogi report with angles.


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 deg
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.

And I pretty much just copied the entire page.