Twist between upper and lower facets

[Turtle]

On some diamond reports, a property of "twist" is measured.

I have included a pic that Garry Holloway provided in this thread:

https://www.pricescope.com/community/threads/template-of-diamond-info.4933/

This seems to be an area that has not been discussed much. What is an acceptable amount of twist between the top and bottom facets? From the pick Garry posted, this particular diamond has a minimum twist of .3° and a maximum twist of 2.3° with an average of 1.1°. Is this an acceptable range? Many vendors quote that the variance between crown and pavillion angles is less than 1° which shows precise cutting. What range of twist in degrees shows precise cutting? Should a dimaond be avoided because of excessive twist? How much is too much twist? Visually, what affect does excessive twist have on the diamond? Poor B-scope images? Poor Firescope images?

Thanks for your help!

 

[Turtle]

Bump. Ok, let me ask another way. If 7 of the 8 facets have around 1° to 2°s of twist and then one of them has 9° of twist, should that be a concern?

 

[pyramid]

I am quite interested in this. I had never heard of it before.
Can CutNut or one of the other experts comment? It sounds as if it may be quite complicated like those drawings Serg deals with!

 

[Serg]

Small twist does not mean good optical symmetry ( The twist between opposite facets is very important)
Big twist does not mean bad optical symmetry
Sarin-OGI twist mistake is more than 0.5( may b 1-2) degree