Differences in Sarin and AGS???

[Garry H (Cut Nut)]

If GIA can not provide an adequate level of accuracy within their own lab to neccessetate that level of rounding then it is very sad indeed.

If that should actually be the case then they have a duty of care to replace their Sarins with Helium scanners.

I do not accept the arguement that they need to allow for other peoples innacurate devices. That is a very poor basis for excessive amounts of rounding.

 

[Rhino]

Date: 8/16/2006 7:17:15 PM
Author: aljdewey

Date: 8/16/2006 5:14:00 PM
Author: Garry H (Cut Nut)

GIA Crown 35 pav 41
can be 35.24 -41.09
or 34.76 - 40.91

I know which I would prefer - and I think you would be able to tell the difference too Rhino.

Amazing.....I think so too, Garry.

LMAO. Garry ... if it were you or I ... MAYBE with a capital "M". The average layman... no way.

 

[Rhino]

Date: 8/16/2006 8:36:54 PM
Author: Garry H (Cut Nut)
If GIA can not provide an adequate level of accuracy within their own lab to neccessetate that level of rounding then it is very sad indeed.

If that should actually be the case then they have a duty of care to replace their Sarins with Helium scanners.

I do not accept the arguement that they need to allow for other peoples innacurate devices. That is a very poor basis for excessive amounts of rounding.

In a perfect world ... everyone would be using it Garry. While I agree with your comments, reality is it isn''t going to happen. This is one reason why I believe GIA has taken the practical approach to this subject that they have. As I have stated, I am for exacting measurements ... quite frankly I prefer it down to 1/1000th of a degree really but you know as well as I that whatever personal standards you or I set for ourselves are not practical for the industry as a whole.

Peace,

 

[Garry H (Cut Nut)]

Date: 8/16/2006 8:48:44 PM
Author: Rhino

Date: 8/16/2006 7:17:15 PM
Author: aljdewey

Date: 8/16/2006 5:14:00 PM
Author: Garry H (Cut Nut)

GIA Crown 35 pav 41
can be 35.24 -41.09
or 34.76 - 40.91

I know which I would prefer - and I think you would be able to tell the difference too Rhino.

Amazing.....I think so too, Garry.

LMAO. Garry ... if it were you or I ... MAYBE with a capital ''M''. The average layman... no way.

I take it that means you agree GIA have a grading system for the average Joe, that just happens to benefit those cutting deeper smaller looking diamonds?

I think that is a shame because GIA is a great organization that does a lot of good for the industry and for consumers.
there is a great interview with bill boyajian in this months Rap mag. It outlines what they accomplished in his 20 year reign. It is amazing. But on the cut grades they stuffed up. This accuracy issue is one pert of the stuff up. DD is the biggest part.

 

[Rhino]

Hey Senor,

Date: 8/16/2006 9:05:49 PM
Author: Garry H (Cut Nut)

I take it that means you agree GIA have a grading system for the average Joe, that just happens to benefit those cutting deeper smaller looking diamonds?

Personally I don''t think its fair to rail GIA for this unless we''re going to equally rail AGS at the same time. Both of these well respected labs allow depths up to 63%. Admittedly I try to avoid depths in the high 62 range but even stones that reach the 62 mark ... if all the angles/percentiles are fine I see no probs. I think the controversy, at least with us fickle types is around the angle combos more than anything. Eh?

I think that is a shame because GIA is a great organization that does a lot of good for the industry and for consumers.
there is a great interview with bill boyajian in this months Rap mag. It outlines what they accomplished in his 20 year reign. It is amazing. But on the cut grades they stuffed up. This accuracy issue is one pert of the stuff up. DD is the biggest part.

LOL... you know how to get a chuckle out of me.

I''ve been swamped the past few days. Once I can escape for a bit I have some interesting stuff for ya but hopefully the DD will be at the symposium so we can look and see some stones together under it so I can demonstrate some facts to ya with it that I know you are mistaken about. Have you taken the time to watch and study my brightness vid again? You may want to recap that mate and study the views under dealer lighting then under DD lighting. Lord willing, you''ll see what I''m seeing and we''ll finally have a meeting of the minds. Gotta split for now. Tata till tomorrow.

Peace,

 

[Garry H (Cut Nut)]

Date: 8/16/2006 8:52:28 PM
Author: Rhino

Date: 8/16/2006 8:36:54 PM
Author: Garry H (Cut Nut)
If GIA can not provide an adequate level of accuracy within their own lab to neccessetate that level of rounding then it is very sad indeed.

If that should actually be the case then they have a duty of care to replace their Sarins with Helium scanners.

I do not accept the arguement that they need to allow for other peoples innacurate devices. That is a very poor basis for excessive amounts of rounding.

In a perfect world ... everyone would be using it Garry. While I agree with your comments, reality is it isn''t going to happen. This is one reason why I believe GIA has taken the practical approach to this subject that they have. As I have stated, I am for exacting measurements ... quite frankly I prefer it down to 1/1000th of a degree really but you know as well as I that whatever personal standards you or I set for ourselves are not practical for the industry as a whole.

Peace,

More evidence of your lack or research Rhino.
Read my comments, and go read why the GIA said they rounded.
Then try to make a valid comment or agree.
But dont waste our time if you never bothered to keep up to date please

 

[aljdewey]

I'll try to be as brief as possible

I have read every word you've said, and that's probably part of the problem. You'll point to the few threads you've hopped on the "minor painting is fine" bus......but the words aren't as loud as actions (usually in the form of waving the WARNING WARNING WARNING banner couched as a public service announcement....the FUD banner).

" Page 2 on this thread is specifically where I answered you. Interestingly enough, regardless of my rather clear words, later in that thread it is again said that GIA is mass grading all painting" -

This perfectly illustrates what happens when you don't pay attention to detail. My comments in that thread had nothing to do with GIA, and I never said GIA is mass grading all painting. My comments replied to one thing: a statement "I don't like painted diamonds"......made by an non-professional enthusiast whose access to real-life stones hasn't been abundant. (No disrespect AT ALL intended to Storm on this; he's in the same position all the rest of us enthusiasts are......not having access to tons of stones in real life).

I do find it curiously odd and even *mystifying* that several esteemed, trained professionals here on PS (Garry, Wink, John Q, Marty.....gee, the list is long, isn't it? ETA: Can't remember if RockDoc is in that group, too, and don't want include him erroneously) all seem to 'misunderstand' your position....and in exactly the same way, too! I consider Wink a very smart guy (and of very high integrity). I wonder where he gets the idea that you're an anti-painting crusader? Yep, it's just odd to me how so many people share the exact same 'misunderstanding' of your position. If I were the one in the position of having to continually reassure everyone, I'd have to stop and wonder what makes them all think that?

For my part, I don't feel the least bit confused about your position. I'm dead certain I know the score on that.

Yes, I do argue for practicality on SI vs. VS.....but for one reason only....there's a HELL of a MONETARY difference! I'm surprised you overlook this very important distinction. Show me two stones that are precisely the same in every (unrounded) way except one is VS and one is eyeclean SI......and both cost the same price. I'd not suggest the SI over VS or VS over SI because there is no monetary OR visual difference.

By taking your argument to its logical conclusions, all eyeclean stones should be "rounded" into one category (maybe VS?). After all, grading is subjective, so it's even more prone to variance than a measly +/- variance on Sarins/Heliums/Whatever scopes, so why bother? Why split hairs over something so subjective that cannot be definitively measured, right? Heck, let's just call em ALL VS! Yeah!

Wrong. There is no visible difference to the unaided eye, but there is a range of standards, and that range of standard affects PRICE. In an interesting parallel, there is also a monetary difference between stones that get the coveted GIA EX grade and those that miss.

(Something that wasn't lost on RockDoc

)

You underestimate the ability of the anal-retentive to accept a "reasonable" margin of error. People do it every day. I think most folks grasp quite well that there is no definitive answer to 'what time is it?' Nearly everyone grasps that "12 noon" isn't an absolute measurement. At the time one thinks it's precisely 12 noon, my watch might read 11:58 and yours might read 12:02. The margin of variation is small enough that anyone being asked "what time is it" could reasonably answer "it's noon".

If I were to show up for a 12:00 pm job interview at 12:02, I would be considered "on time". If I showed up at 12:15, I'd not be considered 'on time.' Gee, what's the big deal? Let's round it! It's only a 15-minute swing in a 1,440-minute day - that's barely more than 1% difference.

If my future paycheck were dependent on showing up on time, I'd prefer not to round, yanno? In fact, if I don't get the job, I'll have to enlighten my potential employer on how my being "late" shouldn't really matter because after all, no one's clock is really right and none of them agree anyway? Who can say for sure when "noon" really was? I'm sure he'll relent and give me the job anyway.

"GIA is providing sufficient data to determine accurate appearance" doesn't answer the million dollar question: "Why are they rounding?" WHO BENEFITS from that decision?

Many professionals on PS, whose opinions I hold in the highest regard, also seem to view GIA's decision to round as a questionable and possible detrimental choice. I'm sure some outside the PS bubble also share those concerns. It's hard for me to imagine why an organization would choose a path with such vocal opposition if there weren't some benefit or payoff to offset that.

Honestly, I could go point by point, but I can only repeat the same thing so many times before losing interest. At some point, you have to agree to disagree, and I'm frankly beyond that point with you, "dear".

It isn't appealing to me to debate the opinion-du-jour knowing that if I wait long enough, it will soon change and become a moot point.

Rhino at 3:46:34 pm: "I still maintain that nobody on this planet would be able to detect the differences with their eyes."
Rhino at 8:44:44 pm: "Garry ... if it were you or I ... MAYBE with a capital "M". The average layman... no way."

I guess somewhere between that 5-hour span, folks in the trade must have seceded from the "nobody on the planet" population.

Better yet, maybe they were "rounded".

 

[aljdewey]

Date: 8/16/2006 9:20:54 PM
Author: Garry H (Cut Nut)

Read my comments, and go read why the GIA said they rounded.

Garry.....link to this?

 

[strmrdr]

In the middle of the ideal range the rounding doesnt matter that much but when you hit the 41 pavilion range and the 40.6 range on the other end it can make a difference.
For example these are both rounded 35-41

 

[strmrdr]

second

So if you buy based on the GIA info which are you getting?
I don''t have a problem with a GIA cert and the diamond I bought has one but I didn''t pay any attention to the cut grade nor the numbers on it.
The helium report was much more useful as is but less so a full sarin report.
With an AGS0 id be more likely to take a chance on it with less additional info than with a gia cert.

 

[strmrdr]

aset for the first

 

[strmrdr]

second

 

[Garry H (Cut Nut)]

Date: 8/16/2006 9:50:37 PM
Author: aljdewey

Date: 8/16/2006 9:20:54 PM
Author: Garry H (Cut Nut)

Read my comments, and go read why the GIA said they rounded.

Garry.....link to this?

http://www.diamondcut.gia.edu/pdf/0805_pg34_39.pdf - that is the article. I do not like any of their arguments.


BTW Thanks for the models Storm.
Joe average might not see the difference - but Joe average buys IGI and EGL paper anyway - because they grade far more diamonds than GIA.

 

[Garry H (Cut Nut)]

Date: 8/16/2006 9:18:22 PM
Author: Rhino
Hey Senor,

Date: 8/16/2006 9:05:49 PM
Author: Garry H (Cut Nut)

I take it that means you agree GIA have a grading system for the average Joe, that just happens to benefit those cutting deeper smaller looking diamonds?

Personally I don''t think its fair to rail GIA for this unless we''re going to equally rail AGS at the same time. Read the article Duh! It has little to do with scanners - and is a huge cop out. Both of these well respected labs allow depths up to 63%. Duh! AGS do not use depth % and GIA can accept stones with nearly twice the AGS system spread reductions - and GIA have never even told anyone how they calculate spread - bad bad bad transperancy. you should know this stuff Rhino - you never bother to read or understand it though. Admittedly I try to avoid depths in the high 62 range but even stones that reach the 62 mark ... if all the angles/percentiles are fine I see no probs. I think the controversy, at least with us fickle types is around the angle combos more than anything. Eh?

I think that is a shame because GIA is a great organization that does a lot of good for the industry and for consumers.
there is a great interview with bill boyajian in this months Rap mag. It outlines what they accomplished in his 20 year reign. It is amazing. But on the cut grades they stuffed up. This accuracy issue is one pert of the stuff up. DD is the biggest part.

LOL... you know how to get a chuckle out of me.

I''ve been swamped the past few days. Once I can escape for a bit I have some interesting stuff for ya but hopefully the DD will be at the symposium so we can look and see some stones together under it so I can demonstrate some facts Here we go again - your Bible bashing "facts" - you simply keep shoving it down our throats that you and you alone know the facts. i am very happy to discuss anything with you - even religion if we must - but I will not discuss anything with anyone who tells me they are going to show me the facts. How hard is it for you to understand how offensive that concept is to anyone who is interested in a topic and learning about the topic? to ya with it that I know you are mistaken about. Have you taken the time to watch and study my brightness vid again? You must be crazy?????????????????? You videos are great entertainment for Joe Average Rhino - but unless you bother to provide repeatability data 9eg angles of filming and background lightin and all sorts of other stuff) then i do not even know why I bothered watch it once 9or twice).You may want to recap that mate and study the views under dealer lighting then under DD lighting. Lord willing, you''ll see what I''m seeing and we''ll finally have a meeting of the minds. Gotta split for now. Tata till tomorrow.

Peace,

 

[Kaleigh]

I am out of my league here, but what if you guys leave the DD out of it. Would that make a difference??

 

[Regular Guy]

Three thoughts:

1) Garry, that article is very helpful:

Date: 8/16/2006 11:18:35 PM
Author: Garry H (Cut Nut)

Garry.....link to this?

http://www.diamondcut.gia.edu/pdf/0805_pg34_39.pdf - that is the article. I do not like any of their arguments.

What I''ve intuited about the rationale for rounding is documented and laid plain by GIA on page 2, end of the second paragraph. Despite their not highlighting it as their main reason (the main reason, they purport, has really been shot down by experts here, with examples from Storm), if GIA were viewed as an organization, one of whose purposes was to protect its membership, then this system is largely designed to cover the ass of its gemologists who have not been asked by GIA to invest in more expensive equipment. Whether or not this is necessary (for its members to buy more expensive equipment) is a separate question, and not necessary to consider (unless you want to guess that GIA has expansionist thoughts, and wants to assert that all their gemologists can do anything, in which case it''s very relevant indeed). But, GIA themselves DOES have state of the art equipment! However, what they state in this paper is that, for the ease and interest in protecting individuals who might seek to check the veracity of data they provide on their certificates, they will only require info be presented that would not be contradict-able by other measures made by other people. In effect, they express concern about presenting data that will not necessarily be exact, but will not be contested, under their rules of measurement. The argument is clear, but this basis for it is disappointing.

2) Painting. Rounding. This thread did touch on rounding, indeed, but had nothing to do with GIA, nor GIA''s practice of rounding. But, Rhino has, with one or two lines (did I bait him, and turn this myself?), had the effect of turning this whole thread to be one about a topic he has found it to be interesting to be contraindicating on. Like another post I had to observe, it seems Jonathan has a pattern of finding it good to have the attention drawn to what he has to say, almost independent of whether what he has to say is good or helpful.

3) Joe Lieberman. Note, he has the goods. Purportedly, he lost for behaviors seemingly opposite to Rhinos (Joe didn''t take the time to get back to some important people; Jonathan does incessantly). Significantly, though, Joe backed the boss. And he went down. Jonathan seems so far to be in no danger of going down, but he seems to be testing us. He is standing up for GIA, and making actual arguments for them in ways that do not make sense. With high irony, he is supporting their use of data that is legislated as poor at the outset by their own reporting standards, while himself, observing the value of investing in technology that is better than most feel is necessary at all. Perhaps this is really pure strategy. But, as others express their frustration responding to Jonathan, at some point, this may come back to bite him in ways one can only begin to try to understand.

 

[aljdewey]

Date: 8/16/2006 10:55:47 PM
Author: strmrdr
second

So if you buy based on the GIA info which are you getting?
I don''t have a problem with a GIA cert and the diamond I bought has one but I didn''t pay any attention to the cut grade nor the numbers on it.
The helium report was much more useful as is but less so a full sarin report.
With an AGS0 id be more likely to take a chance on it with less additional info than with a gia cert.

110% agree with this.

 

[aljdewey]

Date: 8/17/2006 5:58:46 AM
Author: Regular Guy
Three thoughts:

What I''ve intuited about the rationale for rounding is documented and laid plain by GIA on page 2, end of the second paragraph. Despite their not highlighting it as their main reason (the main reason, they purport, has really been shot down by experts here, with examples from Storm), if GIA were viewed as an organization, one of whose purposes was to protect its membership, then this system is largely designed to cover the ass of its gemologists

.......

However, what they state in this paper is that, for the ease and interest in protecting individuals who might seek to check the veracity of data they provide on their certificates, they will only require info be presented that would not be contradict-able by other measures made by other people. In effect, they express concern about presenting data that will not necessarily be exact, but will not be contested, under their rules of measurement. The argument is clear, but this basis for it is disappointing.

2) Painting. Rounding. This thread did touch on rounding, indeed, but had nothing to do with GIA, nor GIA''s practice of rounding. ..........., it seems Jonathan has a pattern of finding it good to have the attention drawn to what he has to say, almost independent of whether what he has to say is good or helpful.

3) (Jonathan) is standing up for GIA, and making actual arguments for them in ways that do not make sense. With high irony, he is supporting their use of data that is legislated as poor at the outset by their own reporting standards, while himself, observing the value of investing in technology that is better than most feel is necessary at all. Perhaps this is really pure strategy. But, as others express their frustration responding to Jonathan, at some point, this may come back to bite him in ways one can only begin to try to understand.

Ira.....from where I''m sitting. you''ve "intuited" right on the bullseye.......on all counts.

 

[Rhino]

Hi Strm,

To bring things a little closer to reality would you please crop your first two images, scale them to roughly 6.5-7mm and put them side by side?

 

[Rhino]

Hi Ira,

To put it all in a nutshell, as simple as I know how ...

I agree that more detail is preferred. I am not contesting this. All I am saying is that with the familiarity I have with the various scanners on the market (Sarin/OGI/Helium) I understand why they have taken the approach they have. That is all. It''s what I stated when I first commented as no two scanners will always give precisely the same measurements. It''s not a reason for people to get concerned and it is not a reason to fight.

Peace,

 

[Serg]

Date: 8/17/2006 12:59:53 PM
Author: Rhino
Hi Ira,

To put it all in a nutshell, as simple as I know how ...

I agree that more detail is preferred. I am not contesting this. All I am saying is that with the familiarity I have with the various scanners on the market (Sarin/OGI/Helium) I understand why they have taken the approach they have. That is all. It''s what I stated when I first commented as no two scanners will always give precisely the same measurements. It''s not a reason for people to get concerned and it is not a reason to fight.

Peace,

re:precisely the same measurements

What is it?

 

[He Scores]

GIA Crown 35 pav 41
can be 35.24 -41.09
or 34.76 - 40.91
I know which I would prefer - and I think you would be able to tell the difference too Rhino.



Gary...Good point. My system does this thinking for you. Should there be actual differentiation in these stones and those differentiations being the only ones, your preferable stone would score a 944 VS the other stone an 880.

My limited retail testing has shown that these figures would provide an instant buying decision on the part of the consumer.


Bill Bray
Diamond Cutter

 

[Garry H (Cut Nut)]

Date: 8/17/2006 12:59:53 PM
Author: Rhino
Hi Ira,

To put it all in a nutshell, as simple as I know how ...

I agree that more detail is preferred. I am not contesting this. All I am saying is that with the familiarity I have with the various scanners on the market (Sarin/OGI/Helium) I understand why they have taken the approach they have. That is all. It''s what I stated when I first commented as no two scanners will always give precisely the same measurements. It''s not a reason for people to get concerned and it is not a reason to fight.

Peace,

You still did not read the article did you?

 

[flopkins]

Date: 8/15/2006 1:56:59 PM
Author: angeline
I appreciate everyone''s replies which are more detailed than I ever hoped for! However as we''re getting into this topic, I have a thought or two... Coming from an experimental physics background, machines used for measurement (and we''re talking MUCH smaller than 1/1000''s of a mm, think nanometers) have a stated accuracy. So if measurements are taken to say 2 decimal places, that last digit is accurate to within +/- .5 of the third decimal place if you get what I mean. eg a measurment of .27mm means .27mm +/- .005mm, or the measurement could be anywhere within .265 to .275.


What I don''t get is

1: why rounding down in weight meas. occurs until the value is >.9

2: if a machine can''t reproduce a measurement consistently to a certain decimal place then that decimal place isn''t accurate and should be rounded according to normal scientific convention as in my small example above. These Sarin machines should have a certain stated accuracy that is reproducible to THAT decimal place. Any further decimal places are meaningless.


just my .02

a

I *still* do not see a good explanation of angeline''s point made here, which I am also wondering. I am also in the science field, if that makes any difference whatsoever, and to me it is silly to report to a decimal that is not in any way accurate - there are very clear rules about this in the scientific field and, in my mind, they are based on entirely reasonable assumptions. (ie, if your instrument cannot repeatably and precisely measure to the thousandth of a unit, you cannot claim that your measurement is accurate to the thousandth of a unit!!)

In some ways I suppose AGS and GIA are of opposite ends of the spectrum on this issue, which is what started the whole rounding debate, but that does not answer the *original point* by angeline???? Why would AGS report to the thousandth decimal if the accuracy of that measurement is not reliable?!!

It doesn''t make sense to me, just as it doesn''t make sense to me that GIA rounds up or down!!

 

[whatmeworry]

Flopkins,
Talking about measuring diamond weight (carat). AGS reports to 3 decimal places, GIA to 2 decimal places. I''m not sure where you get that the AGS 3rd decimal reporting is inaccurate. From GIA''s website, they have a scale than can measure weight down to 5 decimal places, yet they only report 2 decimal places. I would think that AGSlab would have a similar accuarate scale so that 3rd decimal place is probably accurate.

 

[flopkins]

I guess I misunderstood - I was referring to the Sarin data, but I suppose since it is simply a calculated carat weight and used to confirm the measured carat weight the point is moot.

 

[RockDoc]

Decimal places in carat weights are one thing.


Accurate measurements of angles and proportions are a tad different.

While both carat scale and proportion devices are BOTH measuring items of equipment, the tolerances accepted are varying too.

There are carat scales that are capable of weighing a diamond to the third decimal place. I would believe that AGS weighs the same diamond several time to see how repeatible the weight is each time, and that is what they would report.

FOR DIAMONDS, one of the differences between scales which measure weight, and machines which measure millimeters, angles, and then calculate result percentage avererages ( as well as min max measurements) is different.

For weights there exists a multitide of laws, both local, state, county, and federal that require a particular amount of acceptable tolerace, PLUS Scales, gas pumps and the like are tested by legal authorities, to assure this instrumentation is operating within those tolerances, on a periodic basis.

Sarin, OGI, Helium and IMAGEM are not inspected and not required by law to do so. Perhaps in the future this will change, but at the present this is not so. Therefore those reporting such measurements need to clearly disclose what the tolerances or variation are, and what affect the have on the reported data/conclusion.

In an additional viewpoint, I would mention that if GIA wants to round up/down or even sideways, they are entitled to do so. But the details and affect on the results should be truthfully, completely, and accurately stated.

MY position with the GIA cut grade graphic is what is stated underneath it. It says ACTUAL. It can''t be actual if it is averaged and rounded in either direction. That interpretation is not scientific nor is it rocket science to figure out. However, reporting data for which they are paid for, and don''t disclose the appararent details and affect about DOES HAVE SERIOUS LEGAL IMPLICATION and LIABILITY on their part. If not blantant FRAUD, it IS a rather serious breach of implied warranty.

I''m not against GIA''s system. Whatever system they decide to use, is peachy with me, as long as the basis and details are disclosed. Now that GIA''s new CEO is an attorney, maybe somebody who reads this will pass it on, and they will make the imperative changes that need to be made. I am not being ANTI-GIA here, I am hoping they will see this as constructive criticism and advice, and make appropriate and wise decisions to more clearly state what they are reporting. Then knowing the details by someone relying on the report, ( consumers, dealers etc) they know how much weight of consideration to give to the information and results reported.

Rockdoc

 

[RockDoc]

Date: 8/17/2006 6:39:12 PM
Author: flopkins
I guess I misunderstood - I was referring to the Sarin data, but I suppose since it is simply a calculated carat weight and used to confirm the measured carat weight the point is moot.

The carat weight on the Sarin reports is based on a calculated formula.

Interestingly, the person running the scan does enter the actual weight of the diamond, but it is not shown on their reports, which is a tad confusing to consumers.

On stones that I have sent Sarin reports, I often get emails saying, " That is really great, the stone weighs a bit more than what is on the lab report!" Then I have to explain that they got all excited needlessly, cause it is not an actual weight.

SARIN - ARE YOU LISTENING???????? HINT!!!!!!!!!!!

Rockdoc

 

[JohnQuixote]

Date: 8/17/2006 5:31:33 PM
Author: flopkins

Date: 8/15/2006 1:56:59 PM
Author: angeline
I appreciate everyone's replies which are more detailed than I ever hoped for! However as we're getting into this topic, I have a thought or two... Coming from an experimental physics background, machines used for measurement (and we're talking MUCH smaller than 1/1000's of a mm, think nanometers) have a stated accuracy. So if measurements are taken to say 2 decimal places, that last digit is accurate to within +/- .5 of the third decimal place if you get what I mean. eg a measurment of .27mm means .27mm +/- .005mm, or the measurement could be anywhere within .265 to .275.

What I don't get is

1: why rounding down in weight meas. occurs until the value is >.9

2: if a machine can't reproduce a measurement consistently to a certain decimal place then that decimal place isn't accurate and should be rounded according to normal scientific convention as in my small example above. These Sarin machines should have a certain stated accuracy that is reproducible to THAT decimal place. Any further decimal places are meaningless.

just my .02

I *still* do not see a good explanation of angeline's point made here, which I am also wondering. I am also in the science field, if that makes any difference whatsoever, and to me it is silly to report to a decimal that is not in any way accurate - there are very clear rules about this in the scientific field and, in my mind, they are based on entirely reasonable assumptions. (ie, if your instrument cannot repeatably and precisely measure to the thousandth of a unit, you cannot claim that your measurement is accurate to the thousandth of a unit!!)

In some ways I suppose AGS and GIA are of opposite ends of the spectrum on this issue, which is what started the whole rounding debate, but that does not answer the *original point* by angeline???? Why would AGS report to the thousandth decimal if the accuracy of that measurement is not reliable?!!

It doesn't make sense to me, just as it doesn't make sense to me that GIA rounds up or down!!

Flopkins, I understand. I'm sure you're not alone, as there are several layers to all of this.

1. Carat Weight

The Federal Trade Commission requires accuracy to the second decimal place. They also advise that the figure should be accurate to the last decimal place stated.

(c) If diamond weight is stated as decimal parts of a carat (e.g., .47 carat), the stated figure should be accurate to the last decimal place. If diamond weight is stated to only one decimal place (e.g., .5 carat), the stated figure should be accurate to the second decimal place (e.g., ‘‘.5 carat’’ could represent a diamond weight between .495–.504).

You can rest easy on this count, as the carat weight reported on grading documents is derived from a diamond weighing scale that is accurate to the thousandth of a carat.

But...Scanners calculate weight based on the scan, so angular/linear variance results in slightly different weights at the thousandth. Clarity characteristics can also influence weight in ways a scanner won’t pick up, so the scanned number is an estimate.

The ‘Angeline’ solution here

is to treat the lab document's number, derived from a diamond weighing scale, as the figure of authority for carat weight.

2. Angular variance.

This is a horse of a different color.

Sarin's given accuracy is ± 0.2 degrees angular and ± 20 microns linear. This means decisive statements can only be made to the ones column.

If we did this…

CA 34.4- would be reported as 34.
CA 34.5+ would be reported as 35.
PA 40.4- would be reported as 40.
PA 40.5+ would be reported as 41.

This means most near-Tolkowky diamonds would be reported as one of only 4 options: 40/34, 40/35, 41/34 or 41/35.

That’s twice the rounding GIA does with CA and five times done with PA. The feeling is that reporting the average angle to within 0.2 degrees - understanding slight variance as a given - is preferable to cutting off that very-important tenths column.

Now...To make it more complex, remember that overall CA or PA for a diamond is actually an average of 8 measurements (all subject to ± 0.2 degrees).

For clean reporting, every reported average could be followed by the accuracy statement. Example:

Crown Angle: 34.7 ± 0.2 degrees
Pavilion Angle: 40.7 ± 0.2 degrees

...We could also note that it's the average of 8 measurements.

Average Crown Angle: 34.7 ± 0.2 degrees
Average Pavilion Angle: 40.7 ± 0.2 degrees

But...This isn't regulated. Until such reporting is standardized/required in a certain manner the adopted method is as you see on lab documents and most places that provide angular information.

I know this drives science/engineering people batty. My first major was in science so I feel you.

The bright side: Helium has come out with even greater accuracy than Sarin. Technologies continue to improve. The perfect mousetrap has not quite arrived, but the ones we have do scan mieces to useful pieces... I think it's important to state that, in our experience, the machines from place to place (for instance, our Sarin, those of several appraisers who have them and those at AGS) are in agreement as much as they are ever 0.1 or 0.2 degrees off. Obviously, there are exceptions.

Putting this all in perspective, remember that less than 20 years ago we could not even determine these angles and the few measurements we could gauge were done by hand.

 

[whatmeworry]

Rockdoc,
Amen brother! That proportion graphic is incredibly misleading. It leads you to believe that those are the actual measurements. If they want to round up/down when assigning a Cut grade, go ahead. But don''t print the rounded measurements on the graphic. Print what you measured! I think I saw on GIA''s website that grading went through 3 sets of eyes. Anyone know if this applies to proportion measurements? (i.e, scanned 3 times?).