The shell is developed on a flat surface, the position of each plate joint is marked with reference to the top, bottom, and side center lines, which are the first lines placed on this diagram, and the amount of lap for the plates of each adjacent course is marked. All details of rivet and other holes are transferred to this diagram, which is used for marking each shell plate and their butt straps. Each end of each plate is numbered when it is measured up, to insure placing it in its proper location.

The developing of the shell is virtually cutting it along one of its cylindrical elements and unrolling it until it lies flat. This development is made as if the outer courses unrolled without stretching the circumference of their neutral circle, but the inner course neutral circle is supposed to be stretched until it equals the length of the outer course circle in the flat diagram.

In marking off rivet holes around the girth of the shell, care must be taken to space them so that they will be at equal distances apart around the circle.

The distance between centers of adjacent rivet holes is called the pitch of the rivets.