Hello. From a few responses I got to my previous email I understand that I did not formulate my question clear enough. What I meant by "compare two clusterings" is not to find out which clustering is better - this information is usually provided by the k-means algorithm in a form of within-cluster sum of squares. What I actually meant was a measure of how much these two clusters are similar. In other words - if two points belong to the same cluster in both clusterings this means that they are similar. Thanks a lot....