GIA cert gives inconsistant reading with cut advisor

[gingle]

hello, am new to this, and excellent site

anyway, i have a copy of a GIA certificate, 505939102. i am just testing the cut advisor with the figures on the cert.

firstly i put in the crown 14% and pavilion 43.5%, dept 61.5% & table 59%, and got a "2.4 - Very Good ...",
then on the same certificate...
i used the angles of the crown 33.5, and pavilion 41.0, only to get a "1.6 - Excellent..."

what is happening here. could the GIA Cert be inconsistent with it''s own measurements ??!?

anyone else tried this ?

thanks
g

 

[whatmeworry]

GIA rounds the crown angles to every 0.5 degree and the pavilion angles to every 0.2. I wish they didn''t but it''s their method. Even if they didn''t you could still come up with different HCA scores using angles or using %. Anyway 2.4 and 1.6 are both good scores. I wouldn''t be concerned that one score is over 2 and the other is under.

 

[cheradrian]

Quoted from https://www.pricescope.com/tutor/angl_vs_dpt.asp

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:

1. %'s are often rounded i.e. 13.3% crown height becomes 13% or 13.5%.
2. Pavilion depth % when converted to pavilion angle often understates the pavilion angle by 0.15°
3. Scanners are not good at measuring culets; a culet reduces the pavilion depth % but does not change the pavilion angle.
4. 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.

 

[Lorelei]

Hi Gingle

Angles are more accurate so that is the score to go by and GIA round the numbers. Lots on this in the archives if you type in GIA rounding or forced rounding.