Alun, confusing is right! The horizontal mass is what creates the challenge for cartridge matching and why a medium-to-lower compliance cartridge works best in the arm. And, with respect to our more mathmetically inclined forum members, I think it's easy to get *too* caught up in the compliance calculations. There's a lot more going on in the cartridge/arm interactions, and a lot more going on with the cartridge itself, than is reflected just in the compliance/mass calculation data. My philosophy has always been to use this piece of information to make sure I don't have a major mis-match, but not to obsess over it. The only real test is going to be how a given cartridge actually sounds in the arm, to the point of the original question you posed.
To echo Thom's comment on his experience, I expect that any medium-to-fairly low compliance cartridge will work just fine in the ET arm, choose based on the sonic characteristics important to you and the rest of your system.
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