slg47
Ideal_Rock
- Joined
- Apr 4, 2010
- Messages
- 9,667
I am interesting in the differences in reporting numbers between AGS and GIA. GIA averages the numbers and then rounds (listed below). I could not find the description of how AGS reports numbers but I know they do not round crown to the nearest 0.5.
My question is, why the difference in how the numbers are reported? I have quoted below from the GIA website.
My question is, why the difference in how the numbers are reported? I have quoted below from the GIA website.
The GIA Diamond Cut Grading System and the GIA Facetware® Cut Estimator use averaged, rounded values for proportions when assessing diamond cut quality.
The rounding used by the system is as follows:
Total depth is rounded to the nearest multiple of 0.1%
Table size is rounded to the nearest multiple of 1%
Crown angle is rounded to the nearest multiple of 0.5°
Pavilion angle is rounded to the nearest multiple of 0.2°
Pavilion angles ending in odd numbers are always rounded UP, for example 40.7° would be rounded to 40.8°
Star length is rounded to the nearest multiple of 5%
Lower-half (lower-girdle facet) length is rounded to the nearest multiple of 5%
Measurement precision and rounding was determined by considering:
The precision of measuring devices and other measuring methodologies
The practical abilities of most diamond cutters and manufacturers
The differences in cut quality that were found to be consistently distinguishable during our extensive observation testing
These three considerations work together, so we used the highest level of precision that could be applied in all three categories.