AGA/pavilion angle

[mrmarius]

I was reading CutNut's article on this site about the HCA and especially was intriqued by the page talking about how the worst performing proportions in the top grades for various grading systems score on the HCA. Very enlightening. (pardon the pun).

I noticed that one of the columns in the chart was pavilion angle and that the AGA system was in the chart. But I don't see pavilion angle on the AGA cut charts on this site. Is pavilion angle part of the way an AGA cert is arrived at? Or do other measurements of the stone 'force' the pavilion angle into a certain range?

Thanks,
Marius

 

[oldminer]

When we created the AGA charts I used to measure every stone manually. It was easier to be accurate with percentages instead of angles. Yes, the angles are determined by the percentages anyway. There is a direct trigonometric relationship.

Now, angles are all the rage. We have sophisticated equipment to measure them directly. It does not make any difference, but angles are more "in"...There is no actual difference of grand importance.

The difference lies in culet size. The larger the culet the larger the angle at any given percentage depth. The whole culet thing is so minor, but it is why there can be some differences. My tables are based on small to no culet size.

 

[mrmarius]

Thanks for the explanation. It makes sense, what you said about culet size. I can see in my mind the angle getting larger as the culet increases.

To an ex-math-major geek like myself, this stuff is fascinating. I should get engaged more often.