HCA score of .9 vs 1.9 which is a better score?

[FancyIntense]

Can anyone explain what this means?

"Most people prefer stones that rate 1-2 on a scale where: 0-2 Excellent", what does this mean?
I thought a lower score was better? What is the target score? Why isn't .9 a preference if 0-2 is excellent with the lower score being better?
How does a 0-1 score differ from 1-2 while still being in the excellent range?

 

[MarionC]

I'm still not sure what the answer is, but here is a recent thread. I had the choice between a 1.0 and a 2.0 ACA and chose the 1.0. Some folks said it doesn't matter, they will be the same. Maybe it's more of that "mind clean" stuff when you want the best you can get, even if it doesn't really matter in reality

[URL='https://www.pricescope.com/community/threads/ags-000-but-hca-above-2-0.199242/']https://www.pricescope.com/community/threads/ags-000-but-hca-above-2-0.199242/[/URL]

 

[tyty333]

HCA is an elimination tool. Anythingthat scores under 2 is worth a further look (idealscope, ask forum for opinion etc) .

There are stones that do score over 2 that can be nice stones but you need to understand angles/depth/table/lower halves
relationship pretty well (plus idealscope) .

 

[Rhino]

The answer is neither is better. Truth be told you can have a 2.2 with GIA Ex/AGS Ideal optics and a .9 not. I've also had and shot video of 1.7 that got AGS 2 light performance. It's interesting to know an HCA score but I'd never bet my hard earned capital on it.

Rhino

 

[John P]

I'm still not sure what the answer is, but here is a recent thread. I had the choice between a 1.0 and a 2.0 ACA and chose the 1.0. Some folks said it doesn't matter, they will be the same. Maybe it's more of that "mind clean" stuff when you want the best you can get, even if it doesn't really matter in reality

Without more information there is no way to know.

1.0 versus 2.0 is irrelevant. It's like putting two cars on a "HCA radar gun." One is going 55. The other 45. Neither is speeding, so the HCA qualifies them as "safe" drivers, but there is not enough info to know which one is ultimately the SAFER driver. You need to get to know the drivers and put them through many more paces to make a more detailed determination. Even then, there are details that remain unaccounted-for.

The HCA does not take the 40 minor facets into consideration (of 57 total on the diamond). It does not account for cut-consistency. It does not account for 3D optical precision. It does not account for indexing. None of that information is present. The HCA is imagining a "chalk outline" of averaged (sometimes rounded) Table, Crown and Pavilion data, and predicting whether the presumed angles are "safe" or not. That's its intended use, and it's useful in that context; to reject some diamonds - and ID others worth further consideration. It should not be used for selection.

When using GIA reports the output becomes a bit more uncertain: Because of rounding, GIA 57T 34.5C 40.8P could actually be 57T 34.3 40.7 or 57T 34.7C 40.9P. That toggles between HCA 1.3 to 1.8. So a single diamond can vary on the HCA, simply based on how the lab reports the information.

In Context (from a prior thread)

Just imagine that you're trying to get to know someone's looks and personality...

An HCA score is merely like having a chalk outline of the person.
Grading report numbers are like having the person's height, weight and clothing measurements.
An ASET or Ideal-Scope (for RB) image is like having a still photo of the person.
An AGS Platinum "0" in performance is like a panel of judges confirming that the person's personality and looks are solid.
A 3D scan in sophisticated cut-calculation software is like having a video interview with the person.

Eventually, it's a lot of great information. All told it's enough for an experienced cut-specialist to make very detailed performance predictions. But in the end, a live date (dinner & a movie?) will be how you finally judge total personality and looks as you, individually, perceive them.

 

[MarionC]

John, Thanks for the high grade "clarity" on this subject!

 

[John P]

John, Thanks for the high grade "clarity" on this subject!

Nice.

You're VVery welcome!

 

[yssie]

Bah, y'er all wrong.
The most objectively beautiful RB will score exactly 1.35 on the HCA.
Warped girdle is complementary.
Obviously.

 

[Texas Leaguer]

I'm still not sure what the answer is, but here is a recent thread. I had the choice between a 1.0 and a 2.0 ACA and chose the 1.0. Some folks said it doesn't matter, they will be the same. Maybe it's more of that "mind clean" stuff when you want the best you can get, even if it doesn't really matter in reality

Without more information there is no way to know.

1.0 versus 2.0 is irrelevant. It's like putting two cars on a "HCA radar gun." One is going 55. The other 45. Neither is speeding, so the HCA qualifies them as "safe" drivers, but there is not enough info to know which one is ultimately the SAFER driver. You need to get to know the drivers and put them through many more paces to make a more detailed determination. Even then, there are details that remain unaccounted-for.

The HCA does not take the 40 minor facets into consideration (of 57 total on the diamond). It does not account for cut-consistency. It does not account for 3D optical precision. It does not account for indexing. None of that information is present. The HCA is imagining a "chalk outline" of averaged (sometimes rounded) Table, Crown and Pavilion data, and predicting whether the presumed angles are "safe" or not. That's its intended use, and it's useful in that context; to reject some diamonds - and ID others worth further consideration. It should not be used for selection.

When using GIA reports the output becomes a bit more uncertain: Because of rounding, GIA 57T 34.5C 40.8P could actually be 57T 34.3 40.7 or 57T 34.7C 40.9P. That toggles between HCA 1.3 to 1.8. So a single diamond can vary on the HCA, simply based on how the lab reports the information.

In Context (from a prior thread)

Just imagine that you're trying to get to know someone's looks and personality...

An HCA score is merely like having a chalk outline of the person.
Grading report numbers are like having the person's height, weight and clothing measurements.
An ASET or Ideal-Scope (for RB) image is like having a still photo of the person.
An AGS Platinum "0" in performance is like a panel of judges confirming that the person's personality and looks are solid.
A 3D scan in sophisticated cut-calculation software is like having a video interview with the person.

Eventually, it's a lot of great information. All told it's enough for an experienced cut-specialist to make very detailed performance predictions. But in the end, a live date (dinner & a movie?) will be how you finally judge total personality and looks as you, individually, perceive them.

John,
Excellent job of putting this tool into perspective. If you include table rounding in your example I think you will see the range increase even more. In addition you see the qualitative statements falling from Ex to VG. And we are talking here about the same diamond! So that should tell you all you need to know about the ability to derive meaningful insight out of small increments between HCA scores.

I think there is a natural human desire for one tool to do an entire job and that is why people have a tendency to read more into it than it can deliver, or intends to deliver.

I think it is important to keep these same limitations in mind about diamonds that score over 2 as well. The HCA tool is often referred to here as a "rejection tool". While the intent of that advice is to keep people from trying to do too much with it, it is a disservice if people interpret that to mean they should "reject" any diamond because it scores over 2. Especially in the presence of other more complete analytical evaluation.

 

[FancyIntense]

Thank you for the best responses ever! You guys really out did yourselves.

I knew not to rely totally on a score (wouldn't that be nice though), but when not able to view the stone GIA XXX VVS2 (from trusted online store) until it's paid for and unable to buy two at once to make a comparison, I wanted to make sure my narrowing down was an educated one. Not to mention the return process turn around can be time consuming. I know you guys have heard this all before.

I didn't put the stats on the stones which was not helpful.

 

[MarionC]

John, Thanks for the high grade "clarity" on this subject!

Nice.

You're VVery welcome!

Dfl response