I did this sketch just for fun for another thread. It shows the adjustment range from full extension down to minimum extension, and the rough steps available until the full vernier range where there is a consistent 1/8" length change available (starting at 1-1/2" retracted). Longer than that point the adjustment increments are all over the place (1/2", 3/8", 1/4"), which was relevant to my boat because I stood the mast up pretty near vertical but that put the adjusters at full extension initially. The smallest reduction I could get at first was the 1/2" change, which is where it is now (the uppers; the lowers were in the vernier range already).
Eventually, two holes line up for every 1/8" change (last two iterations, plus all those in between but not shown). My backstay has both a vernier adjuster and a turnbuckle (from the PO), so to minimize the number of joints in that connection that are making things flop all over while I'm trying to pin the backstay, I shortened the adjuster and put two pins in it, and lengthened the turnbuckle so the backstay is slack for pinning but easily tightened to take the slack out prior to sailing. I
should just make a new backstay that's long enough to eliminate the turnbuckle and adjuster, and use a Johnson lever for quick tensioning, but I have other projects more pressing.
Posted just because I already had it, and found it interesting.
