What makes the difference between a good one and a great one ?
To answer that question correctly, you have to know what a good Arm is, what it cannot do and why a great one is a great one.
Most think, their Arm is a great one (no matter how bad it really is or what flaws it has)... well, what's the difference?
A great tonearm is dynamically balanced, will show rigid construction, fast transmission of energy, rigid bearings which are able to further transport the energy away from the arm, precise geometry, tooling and knowledge of materials.