For an average setting with the boom head in the middle of the boom cut out, choose the average setting marked on the sail, in this case 164cm. The indicated min and max boom lengths are for the shortest and longest possible boom setting, the longest setting is boom head at the top of the boom cut out and high wind setting, the shortest is for the boom head at the bottom of the boom cut out and the sail set for low wind. With the boom head set at the middle of the boom cut out, the range is 2cm less at either end.