GOG Cert numbers and the HCA

[Spark Lee]

In this thread, we were asked to compare a couple diamonds. In doing so, I thought I''d run the HCA numbers, and I was shocked at what I found:

For this diamond, I could find six sets of numbers, and their associated HCA scores:

AGS PGS Report: (has a Sarin logo on it)
Table 56%
Depth 61.6%
Crown 34.2%
Pavillion 41.2%
HCA: 3

Numbers on the page:
Table 55.55%
Depth 61.60%
Crown 34.15%
Pavillion 41.07%

HCA: 2.3

Megascope:
Table 54.4%
Depth 61.4%
Crown 34.0%
Pavillion 41.1%
HCA: 2.1

GIA Facetware:
Table 56%
Depth 61.60%
Crown 34.0%
Pavillion 41.0%
HCA: 1.4

AGS Lab Report:
Table 55.3%
Depth 61.5%
Crown 34.0%
Pavillion 41.0%
HCA: 1.3

Helium:
Table 55.9%
Depth 61.3%
Crown 34.03%
Pavillion 41.03%

HCA: 1.3

I''m trying to come up with a more coherent question than "WTF mate?"...

I understand there will be some variation from one measuring device to the next, but seriously? How can I use an HCA score of 2 as a cutoff point if the same diamond can pull such drastically different measurements? I would even understand if one out of the five sets of numbers was an outlier, but three outliers out of six?

Note, I''m not knocking the HCA in any way. It can only go by what you tell it. My beef is with the devices/people generating the numbers.

Not to mention, where the heck is GOG getting the numbers it lists on its page? I can''t find that 55.55% table on any report.

Basically, now I''m afraid that all the diamonds I''ve rejected due to 2+ HCAs might not be so bad if the cert numbers aren''t accurate and precise.

So what gives?

 

[diamondseeker2006]

There are more knowledgable people here to answer this question than me, but I will tell you, for example that GIA rounds some of the numbers. And helium scans are more accurate than some of the other scans such as Sarin. So on a very basic level, you get slightly different numbers depending on the device doing the measuring and the way the numbers are reported.

You don''t need to put GOG hearts and arrows stones through the HCA because they have already been evaluated in a more extensive manner (such as the AGS light performance). You use the HCA on stones from vendors that do not provide the extensive information that GOG and a few other vendors do.