What we used to do when setting up Lightnings for racing was to use the main
halyard to hoist a tape measure and check for the mast being straight and
properly raked. We used the top corners of the transom and the chainplated
for the shrouds to adjust the turnbuckles. No plumb bobs, cosmic rays,
satellite triangulation, animal magnetism or even a tension gage for the
stays are necessary although the tension gage might be advisable for initial
setup of the rig. You could even check from the waterline to be absolutely
sure the mast was square with the world and not just the deck; but you'd have
to mark it first. Then you'd need a 'waterline finder' or a wetsuit and a
grease pencil...
Bill de Ment
P-15 #1044 'Sukoshi'
Eagle, Idaho