Hi, Larry: I think I have an answer to your question. After my last post, I had the nagging feeling that I had read something recently about the JMW arm, so I looked through some recent issues of Stereophile, TAS, and Listener. I found the article I wanted - a review by Art Dudley in the May/June issue of Listener of the Aries / JMW arm combo. According to Dudley's article, the effective mass of the JMW-10 is 11 grams. Since Dudley has been a personal friend of Harry Weisfeld and his wife Sheila for a number of years, it is safe to assume that Dudley has his facts straight. Hope this helps you. I would like to request some info from you in return: what is the resonance computation formula that you use?