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Simple mathematics....

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diagem

Ideal_Rock
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Interesting view....



"The Difference One Decimal Can Make
“A calculation on the back of an envelope will show that every year the worldwide diamond industry loses approximately $100-$135 million because of the (highly unjustified) practice of gemological laboratories only giving a diamond''s weight to the second decimal point. Every third decimal point that weighs less than 0.009 is rounded downwards. If you have a $3,000 p/c stone that weighs 0.505 carat, the GIA’s or any other certificate will say it weighs 0.50 carat. In this instance the seller loses $15 since in fact, the true price for the stone should be $1,515. The seller is losing almost 1 percent of the value!......”


http://www.idexonline.com/portal_FullEditorial.asp


 
err... what about if the lab rounds up the weight? That's some weird logic.

Even his math is wrong, 0.505 should be rounded to 0.51 while 0.504 down to 0.50.
 
They must set prices to take that into account.

As a result the customer who buys a 1.019 ct gets a slightly better deal than the customer who buys a 1.010 ct diamond for the same price.

I'd guess the price of these two diamonds would be the price set for a 1.015 ct diamond.

Or am I not interpreting this correctly?
 
Pooooor diamond sellers!
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My diamond is exactly 2.00 carat. Now you have got me thinking if it is actually 1.999 or 2.008?
 
loverock

Don't forget the calibration error potential of the scales that weighed the diamond.
While I expect that the scales are regularly calibrated, the calibration can drift and about 99.5% accuracy is probably more realistic.

So when your diamond was weighed, the scales might have read 1.995 and got rounded up to 2.00.
...and if the scales were reading 0.5% high at that time they measured yours as 1.995ct, your stone might actually be as light as 1.985ct.
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.....and what happens if you cause a tiny chip in the girdle that loses you 0.01ct off a 2.00ct stone and turn it into a 1.99ct stone?
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Date: 8/20/2009 3:01:26 PM
Author: Stone-cold11
err... what about if the lab rounds up the weight? That''s some weird logic.

Even his math is wrong, 0.505 should be rounded to 0.51 while 0.504 down to 0.50.

"...What is interesting is what the U.S. Federal Trade Commission has to say about the issue. It doesn’t comment on individual laboratories. In its guide to the public, it writes, “If the weight is given in decimal parts of a carat, the figure should be accurate to the last decimal place. For example, ‘0.30 carat’ could represent a diamond that weighs between 0.295 - 0.304 carat.” On a certificate the 0.295 carat, 0.296 carat, 0.297 carat and 0.298 carat would be rounded down to 0.29 carat. It seems unreasonable that certificates provide a lower weight than required by the FTC. It is simply money thrown away."
 
Interesting, DiaGem.

So 0.9999 would get the digits chopped-off and still be reported as 0.99.

....and 1.0099 would also be chopped-off and reported as 1.00.

Basically, you're saying that everything is "rounded-down" and not "rounded nearest".

I've noticed a number of diamonds with AGS certs with weights given to an extra decimal place, yet the vendor rounds-down the weight - so an AGS-cert stone of 1.019 would be listed as 1.01 in the retailers inventory.

I think that's the best approach, since it prevents 0.995ct stones being "over-sold" as 1.00ct due to rounding nearest.

Besides......the diamond industry gets it's fair share of extra profits by churning out sub-standard cuts that maximise weight.
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Date: 8/20/2009 5:09:59 PM
Author: FB.
Interesting, DiaGem.

So 0.9999 would get the digits chopped-off and still be reported as 0.99.

....and 1.0099 would also be chopped-off and reported as 1.00.

Basically, you're saying that everything is 'rounded-down' and not 'rounded nearest'.

Weighing results of 0.991 ct, 0.992 ct, 0.993 ct, 0.994 ct, 0.995 ct, 0.996 ct, 0.997 ct and 0.998 ct are without exception rounded down to 0.99 carat while only the result 0.999 ct is rounded up to 1.00 ct and on and on....


I've noticed a number of diamonds with AGS certs with weights given to an extra decimal place, yet the vendor rounds-down the weight - so an AGS-cert stone of 1.019 would be listed as 1.01 in the retailers inventory.

I think that's the best approach, since it prevents 0.995ct stones being 'over-sold' as 1.00ct due to rounding nearest.

Besides......the diamond industry gets it's fair share of extra profits by churning out sub-standard cuts that maximise weight.
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Cool thread DiaGem!

I believe there is a practical aspect to this.
We''d need to accurately weigh to the fourth decimal place to have a system using three digit weights.
In other words, we''d still need to round- a stone that weighs 2.0009 would be a 2.001ct

Then you get into how accurate scales are.
Using the two digit system most companies have scales that weigh to the third decimal place.
Due to limitations of stability, it''s not reasonable to assume that scales of such accuracy would be widely available.
At that level, you''d need an extremely stable purpose built base.
Todays carat scales are fairly accurate to the third decimal place, and can be used in a typical desk, or counter top. I see these as physical limitations.

I''ve never had a digital millimeter gauge that gave the exact same measurements as GIA. ( to the second decimal place.)
 
Date: 8/20/2009 5:09:59 PM
Author: FB.
Interesting, DiaGem.

So 0.9999 would get the digits chopped-off and still be reported as 0.99.

....and 1.0099 would also be chopped-off and reported as 1.00.

Basically, you''re saying that everything is ''rounded-down'' and not ''rounded nearest''.

I''ve noticed a number of diamonds with AGS certs with weights given to an extra decimal place, yet the vendor rounds-down the weight - so an AGS-cert stone of 1.019 would be listed as 1.01 in the retailers inventory.

I think that''s the best approach, since it prevents 0.995ct stones being ''over-sold'' as 1.00ct due to rounding nearest.

Besides......the diamond industry gets it''s fair share of extra profits by churning out sub-standard cuts that maximise weight.
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I agree, it makes more sense to round down to the benefit of consumers than it does to round up in hopes of scraping every penny of profit out of a deal at the expense of the public. Scale calibration fluctuations, seemingly subtle things like a little air movement in a room can have dramatic effects on carat weight. No doubt the cutters cry when a diamond weighs 0.995 carats on the lab scale when they''re hoping for a 1.00(anything) so that they can benefit from the price increase which occurs between the 0.99 - 1.00 carat marks, but that''s life.

And let''s not forget that when a diamond does miss the mark by a hair that the cutters are going to make up for it by decreasing the discount given to the dealer, so what''s all this whining about anyway?
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As a FYI - and I know many of you know this - AGS prints ct weight down to the 3rd decimal place on its reports.
 
Date: 8/20/2009 4:19:38 PM
Author: FB.
loverock


Don''t forget the calibration error potential of the scales that weighed the diamond.

While I expect that the scales are regularly calibrated, the calibration can drift and about 99.5% accuracy is probably more realistic.


So when your diamond was weighed, the scales might have read 1.995 and got rounded up to 2.00.

...and if the scales were reading 0.5% high at that time they measured yours as 1.995ct, your stone might actually be as light as 1.985ct.
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.....and what happens if you cause a tiny chip in the girdle that loses you 0.01ct off a 2.00ct stone and turn it into a 1.99ct stone?
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hmmmm

.001ct below advertised total weight = ($1000000.01 fine and 180 days in jail)x number sold
I like that math better.
 
can you tell that under carating is a pet peeve of mine?
 
Strm - Did you know that in the 1800s bruters (they were called cutters then) were given diamonds attached by cement to wooden handles and a box to catch the dust coming from the rubbed-together diamonds... At the end of the day all would be weighed. If they failed to catch the proper amount of dust they were fined for it. The life of a cutter's career was often shortened because their hands and knuckles finally gave out. "Bruting" earned its name literally.
 
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