bow-tie percentage?

[ephemery1]

I''ve been on an oval hunt, and talked to Mark T. yesterday (really great experience with him thus far, incidentally) about a stone he is checking out for me on Monday. He said it has a bow-tie percentage of 10%... which is supposedly minimal. Anyone else heard of bow-ties referred to in percentages before? Any thoughts on one that would be 10%? Thanks!

 

[FireGoddess]

I have never heard of this but I would love to hear more. 10% as compared to what? In what lighting conditions? I''m intrigued.