sentence: We took the max ( D ) − D as the final measure so that a larger value is preferred.We also measured the average Jaccard index of all the pairwise best matching cluster centers : ( 8) Jk = 1R2 ∑ q =p +1 R ∑ p = 1R − 1 ∑ j = 1KJ ( Sjp , Sjq ) where S is the set of zinc fc ‐ shells clustered as cluster j in repetition p , and ( 9 ) J ( Sjp , Sjq ) = | Sjp ∩ Sjq | | Sjp ∪ Sjq | The average Jaccard index measures how well the same set of zinc sites are clustered into the same cluster between repetitions .