I actually spoke to one of the technicians at Clavis, who was really approachable and told me lots of interesting stuff! They make the gauge that Ducati use to tension the testastretta engines. I think he said it's an optical pickup head on the gauge.
He popped away and came back with the info on the 4v engine. Tension is checked on the lower run on the horizontal cylinder and on the left side run on the vertical. (I'm no technical expert at this so any claims made in this thread have no actual factory or otherwise guarantees ok!).
Jeez, I sound like a lawer
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Keith, I like your bit about just taking the readings of the oscillations, regardless of the type of mic. used, kinda makes sense to me when put like that.
I wish Clavis would just sell me one of their heads so I could plug it into my computer!
Pete.