HCA score decreases ,visible difference?

[rosy]

Hi,
My question is if you have a score of 2.4 on the HCA, at what point as the score drops lower will you begin to actually see a difference in the diamond with your naked eye? 2, 1.8, 1.5, etc.? Thanks!

 

[Garry H (Cut Nut)]

Probably at 1.8.
Definiteley at 1.0 to 1.5.

Assuming equivalent symmetry etc