All good info but really...it's not that difficult to do.
Lay on your back, feet facing the bow, looking up the mast to see the straightness of it port to stbd. Adjust until straight with moderate tension on the shrouds or stays. Next lay on your back with your feet off the beam while looking up the side of the mast to check for bend for and aft. Adjust acordingly until straight with moderate tension on shrouds and stays...done. I've been doing it for 15 years this way.