You don't need to do all that with boards and protractors, etc. You just put the bike upright with the inflated rear wheel touching and perpendicular to a wall. Then measure all distances from the wall and the floor. So reach is the difference between the distance from the wall to the bottom bracket and the distance from the wall to the top center of the head tube. And so on. Stack is the difference between the height of the bottom bracket center and the height of the top center of the head tube. Easy.