The MF-2 mainsail is the original "set it and forget it" tuning system. Once you have your Lightning set up to the North Sails MF-2 tuning specs you don't have to move any blocks or change any shroud tensions to get maximum performance. The MF-2 tuning system relies on utilizing your jib halyard (wire) to depower or power up the rig. Maximum wire tension in big breeze and softer tension in light air keeps you thinking less about whether you have the right tune and more on the tactics and strategy of your race.