HCA Question

[kenny]

If I understand correctly the HCA calculator here on Pricescope does not factor in girdle thickness because it is not the advanced version.

Does this mean it assumes a girdle of 0%, and is most accurate on stones with the thinest girdles?

Please correct me if I misunderstand.

 

[pricescope]

no, it assumes medium girdle. Advanced version takes girdle thickness into consideration and penalizes very thin or thick girdles.

 

[valeria101]

Date: 5/28/2005 3:18:56 PM
Author:kenny

Does this mean it assumes a girdle of 0%, and is most accurate on stones with the thinest girdles?

Table % and the two angles (crown and pavilion) are the crucial factors there. Girdle thickness has any contribution when percentages are used instead of angles: in that case, the system needs to compute angles from the % given and girdle thickness influences the results.

Since you do not input girdle thickness into the HCA, it is "guessed" by comparing the total depth resulting from table & angles with the depth % you give. When this result is extreme (as leonid says) the HCA does not procede to compute the score and gives warning.

However, this may be a real problem of the diamond in cause or (more likely) the measurements. The numbers involved are small and measurement error present, so sometimes this girdle thickness deduced by the HCA doesn''t quite fit that mentioned on the lab report. Between the two, the lab report winns, because girdle thickness given there comes from direct measurement, not approximate calculation.

As far as I know...

It is far easier to talk about one diamond in particular than give an exhaustive critique of the system !

Btw... by similar reasoning, the "spread" score given by the HCA doesn''t always fit the measurement on the lab report. It is allot easier to compare diameter size with the standard for a give weight (and wish for something within .2mm of it), than reality-check the "spread" score deduced from table and angles by the HCA.

 

[Mara]

as Leonid noted it takes medium girdle into consideration, so if a girdle was thick then the HCA score would not show that...yet.

 

[Garry H (Cut Nut)]

HCA does use the depth % to calculate the effect on spread.
Here are 2 examples

64.2% depth, 57% table, 34.5° crown angle, 41° pavilion angle HCA 2.2 Spread Good
58.9% depth, 57% table, 34.5° crown angle, 41° pavilion angle HCA 1.6 Spread Excellent

You can not enter depth % 64.3% and get a result because HCA tells you the stone has a girdle that is too thick.
You can not enter depth % 58.8% and get a result because HCA tells you the stone has a girdle that is too thin (it would be a negative value)

 

[valeria101]

Date: 5/28/2005 6:54:21 PM
Author: Mara
as Leonid noted it takes medium girdle into consideration, so if a girdle was thick then the HCA score would not show that...yet.

ups... posting at once with Garry...