reef line main
On the aft end of your boom on the opposite side where the block is should be a small bracket maybe an 1 1/2" long 1/2" wide 1/2"loopin it. Anyway, the line should run from this bracket,up the leech[back side of sail]to where the grommet is[at reefing height] thru the grommet, down thru the turning block[on oppositeside of boom that the bracket is on]and up to the cleat[leave the line with a little slack in it so as not to affect the sail shape, and make it long enuff to tie off].In other words do your measurements with the mainsail up.hope this helps.