A few years back, Mitch Booth showed Dave and I how to tune our Tiger mast to match the luff curve of the main. He had us flip the boat on it's side, connect the main on the halyard hook, connect the downhaul, and mainsheet and sheet in hard as though you were going up wind. Note - the main is not in the luff track, it is outside the mast. Look at the luff curve of the sail, and compare it to the curve of the mast track. Adjust your diamonds and spreader rake accordingly to get them to match. That is your new "base setting". We found that we were carrying anywhere from 800 to 1,000 lbs of diamond tension to get some mainsails dialed in.