DCI Megascope report makes no sense! Math error?

[Racer811]

I got a Megascope report from Diamond Cutters International, and I''m struggling to understand how these numbers can be right. Here''s the problem:

Table = 55.0%
Crown Angle = 34.2 deg
Crown Height = 13.3%

My understanding of trigonometry (and the HCA) says that this is impossible, no??

The other dimensions are:
Pavil Agle = 40.7 deg
Pavil Depth = 43.1%
Culet 0.4%
Tot Dep = 57.7%

If you fix the crown angle (I think it should be more like 30.6 deg) then this seems to be a poor cut. Hmmmm...

 

[icelady]

Hi Racer811,

Just wanted to bump your post for some attention!

 

[pricescope]

there could be some measurement errors for both angle and crown height.

CrownHeight = TAN (crownangle) * (100 - table)/2 = TAN (34.2°) * (100% - 55%)/2 = 15.3%

There are several factors that affect accuracy of the measurements...

 

[Garry H (Cut Nut)]

Yes you are correct.
But it is even worse than that.

Using the % data, the crown angle is 30.55, the pavilion angle is 40.9 and the stone has a negative girdle of -0.3% which means that the stone will be 16 sided and not round with dangerous knife edged girdle. (i.e. seriously warped)

I have seen "made up" scan information like this before. One needs to be vigilant.

 

[mdx]

----------------
On 10/22/2004 9:07:07 PM Garry H (Cut Nut) wrote:

Yes you are correct.
But it is even worse than that.

Using the % data, the crown angle is 30.55, the pavilion angle is 40.9 and the stone has a negative girdle of -0.3% which means that the stone will be 16 sided and not round with dangerous knife edged girdle. (i.e. seriously warped)

I have seen 'made up' scan information like this before. One needs to be vigilant.----------------

Not sure if it’s the diamond that’s seriously warped, The creator of the “made up” report could be a contender.

Johan

 

[Racer811]

Thanks a lot Garry, this confirms my suspicion. Doesn't this seriously impugn the credibility of DCI?? I find this amazing that can get away with this and still have any kind of reputation. Maybe I'll become the anti-DCI crusader. Anyways, here's the Megascope report in question. I'm really not happy.

 

[jasper]

The girdle plot has quite a dip in it.

Perhaps the table is tilted?

If the MegaScope measured the crown height
on the high side of the girdle,
it is possible that the crown angle is accurate.

-- Jasper Paulsen
-----------------
[email protected]
www.folds.net/diamond

 

[Garry H (Cut Nut)]

Yup the stone is seriously warped.
I can not understand the thickness of the girdle plot vs the stated range from 0.7% to 1.3%.

Clearly the pavilion depth, with a culet of 0.4% would be deeper than 43.1% if it had no culet. So the pavilion angle and the depth % do not match?

Either this scanner is a heap of **** or the scan has been reworked in photo shop.
It is possible that as Jasper has said - the very wobbly girdle and Ogi's "averaging" algoritms have been thrown out further than they ever thought possible. Certainly this is not a diamond anyone would want to own.

 

[Garry H (Cut Nut)]

This is from Ogi's website - it is a demonstration of their supposedly newest more accurate scanner's ability to display a web viewer (catching up with what Sarin have had for 3 or 4 years).

I have often said that Sarin is more accurate at measuring angles than Ogi because of the way the models are built. In this image you can see that there is some mathematical calculation that has made the grey facet images line up - even though the actual scanned facet bones are way off. Sarin too have an averaging function, which I would prefer they dropped because when we examine diamonds that are scanned and imported into DiamCalc, it is better to take and use the most pure, least doctored information. For that reason Sergey's Helium scanners will make a clean sweep of anyone who is serious about using 3D models to analyze cut quality.

The type of inaccuracy displayed here probably gets its error factor from fact that the scanner has assumed all the facets point symmetrically away from each other (i.e their azimuths on opposite sides of the stone are 180 degrees away from each other). What this means is the scan has made the stone the symmetrical. This is a disaster.