Re: Rig cable tension
I believe most riggers do a static tune to about 10% breaking strength of the wire, tighten a little by eye and feel, then sail it in 15 knots and dynamic tune from there. I've checked tension under sail then tuned at the dock using the "tuning fork" method for equality ( ya rap the shroud with your spike and adjust till the pairs ring the same note). Takes a few more checks and adjusts to get things fine tuned.
Oh, did I mention you also have to keep checking to make sure you are still "in column" (mast still plumb and true in English) etc. etc.