Dear Nikola,
I find it harder to see (and hear) things as time marches on. But I try.
As you say, the protractor is only as good as the widest tolerance. Which is my point. As DT says, spindles vary, by 0.25mm. So there we actually have a number. But he asks
Why use a super accurate protractor?So super accurate means that "best" is sonic performance, as opposed to physical performance.
Simply because it helps to get the best (read: best sonic performance) out of your cartridge/tonearm.
In other words to continue DT's analogy, if Michael Schumacher could drive his Ferrari with the old beetle tyres faster than Dertonarm using the expensive ones, then are his tyres better than DT's? Would we buy them?
Wouldn't we rather look at the description of the tyre's performance? The reasons we might choose it for a Ferrari, why it might be suitable.
The analogy here is to the protractor's performance. How accurately can it set up the arm. Will it be within 1mm, 0.5mm, 0.1mm in overhang? Will it be within 1degree, or 0.5, or 0.1? Mounting distance? And how repeatable is it?
I'm not saying Dertonearm's protractor isn't precisely made, or can't give good results, just that neither he, nor anyone else, gives a specification for protractors, one of the few areas in hifi where that is the case. If it was an amp, would manufacturers get away with saying how loud it goes depends on how well you set the volume control?
Perhaps if someone said it was precisely made? Or said it looked impressive?
Or maybe I'm getting too old and too cynical.
John
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