First make sure that your trailer is level, and your boat is level. I started by marking the same measurements from the stern on both sides, and then continue with one foot increments as far as I could get to the bow. I then ran some 1" screws in that flange that is left on the sides after you take out your floor. Pull your line (I used nylon fishing line) across at every 1' you put the screws. I then snapped a chalk line along the bottom close to where the old ones were and used a level to mark the floor and the string at all the one foot locations. Start pulling measurements and transfering them to your lumber. To get the angles of the bevel cut you can measure over the width of your new stringer (mine was 1-1/2") on the floor and the string above. Then take that differance and draw to lines that extend out 10", then use a speed square to get the deg. I probably didn't explain that to well, but it worked for me. I just used a circle saw and kept adjusting the bevel as I cut. Here are some pics that may or may not help...good luck.