Angle vs % - HCA results differ?

[highlander14]

Hello all,
I have just a quick question that has probably been answered before:

Is there a more accurate parameter to use for crown and pavilion dimensions in the HCA calc? Using the cut adviser for HCA result, the results differ slightly depending on whether the angle (°) values are used vs. the percentage values from the GIA/AGS reports.

I assume the cause for the different results is errors in rounding on one of the measurements. Is one set of values more subject to rounding than the others?


Example:

Depth 62.7
Table 55.0
Crown 15.5%, 34.0°
Pavilion 44.0%, 41.2°

4.4 HCA using %
3.1 HCA using °
(I realize that this example is not of a quality cut. For HCA scores less than 2.0, I get the same discrepancy although the difference is less pronounced.)

I suppose it does not matter too much since the HCA value is intended to be used as a filter to weed out the good from the bad. However, before I get too carried away with HCA results I thought I should understand which values are preferred in the calculation.

Thanks for educating me!

 

[stone-cold11]

The is because of the rounding off of the numbers. GIA rounds the angles. If you use %, the HCA uses the numbers and convert it back to angles, this will have some rounding error too. Use the angles, it is more accurate.