Most bowls will perform one function better than another whether spinning or hitting. Some do both well but this is rarer.
Our grading system is as follows, we use a 6 to 10 grade for all the qualities below. Look for 9's to 10's for a great bowl.
Keep in mind that sometimes a bowl does one thing well and another thing not so well such as a bowl with a great dominant tone, but a silent or non-existent harmonic note.
Just because the bowl gets a 7 score for its harmonic be sure to look to the other sections to get a better view of the bowls complete sound value.