TIC or BIC on the Holloway Scale?!

[John P]

I'm curious, is the source of this uncertainty understood? Is it actually an accuracy issue (which could potentially be overcome by improved calibration techniques) or a limitation in the measurement precision (reproducibility issues due to randomly distributed fluctuations)? It may be possible to improve precision by making repeated measurements (and averaging, if normally distributed). Or is the limitation due to quantization error (i.e., sensor resolution)?<ENGINEER MODE = OFF>

It's precision (fluctuations): These are non-contact scanners. The diamond rotates on a stage while the facets are mapped. Video example here. That's where fluctuations may occur. Connecting this to diamond cutting precision; our fundamental proposition requires us to eliminate all ground vibrations. We sink the legs of our polishing mills several feet into foundations. We even removed ourselves from areas with traffic/airports, because a truck passing by or plane landing in the area will affect the precision of our crafting goals. Logically, the same kind of fluctuations can affect the subsequent scans.

And admittedly, we're wine snobs in all of this. In the bigger picture the stages, lighting modules and lenses are tremendously accurate (IFF the stages are spotless and you regularly calibrate). It's evolved to the point where symmetry grading of facet meet points, historically done by the human eye, has shifted to scanners. As for your suggestion of repeated measurements, that's happening. When we request an improved scan the lab frequently has a backup scan (or two) that turns out to be more representative. But in some cases we either remove the diamond from market and ship it back, or just accept "close enough."

Swerving back to the GIA topic: Proportions output is far simpler than generating detailed 3D imprints. I'd argue that normal scans are already "close enough" to publish averaged 2D proportions to within 0.1 degree.

BTW, when I grow up I want to be an engineer.

 

[flyingpig]

I do not see GIA's rounding system has anything to do uncertainty and precision of scan technology. It is just to cater to its customers (diamond suppliers and cutters). The rounding system makes no sense.
Nobody in scientific field uses such system; at least I have not read any legit scientific article with such bizarre practice.

 

[drk14]

Swerving back to the GIA topic: Proportions output is far simpler than generating detailed 3D imprints. I'd argue that normal scans are already "close enough" to publish averaged 2D proportions to within 0.1 degree.

Beyond GIA's practices, would there be any value (for purposes of evaluating light performance) in having higher precision (lower uncertainty) in the angle precision, if it could be achieved (with minimal overhead)? Or is +/-0.1 degree sufficient for all practical purposes?

 

[drk14]

I do not see GIA's rounding system has anything to do uncertainty and precision of scan technology.

It may have more to do with the variability in the measured angle across multiple facets due to imperfect symmetry. If the standard error of the mean is sufficiently large, then it may make sense to express the mean value to a precision that is lower than the measurement precision. Would be nice if the reports stated the standard deviation or standard error, actually...

Anyway, I think I'm threadjacking -- apologies to OP!

 

[John P]

Beyond GIA's practices, would there be any value (for purposes of evaluating light performance) in having higher precision (lower uncertainty) in the angle precision, if it could be achieved (with minimal overhead)? Or is +/-0.1 degree sufficient for all practical purposes?

It's quite sufficient for assessing static brightness, leakage and contrast, and drawing some logical conclusions about tilt and dispersion, in order to repeatably place a diamond within a basic performance grade. But research and eventual grading of compound mirror integrity, spectral fan output and intensity/visibility (esp. through a given range of motion) requires a higher level of precision.

 

[bmfang]

Swerving back to the GIA topic: Proportions output is far simpler than generating detailed 3D imprints. I'd argue that normal scans are already "close enough" to publish averaged 2D proportions to within 0.1 degree.

If labs like AGS can provide proportions to 0.1 degree on their reports, it befuddles me why GIA doesn't do so. On the bright side, this means that when I have work colleagues or friends ask me what diamonds they should be purchasing, I'll just have to recommend them to online houses who primarily have AGS graded stones (ie Whiteflash, BGD, VC and of course, CBI-HPD).

 

[Garry H (Cut Nut)]

Question I found a diamond with the following:

Depth 62.1
Table 58
CA 34
PA 41.6

Only the PA is a little off your grid but yet the diamond rated a 5.7 on the HCA scale, how did that happen?

41.6 is very deep. It works with a crown angle of 30 degrees, but there is then a greater chance of chipping and less fire or colored flashes