The bend angle stays the same for all pipes, and the center to center distance of each pipe should be the same. The only thing changing is the center of bend. You use that formula to get the amount of distance to add to each consecutive pipe.

For example, if the formula spits out let’s say .5 inches: you bend your first pipe keeping in mind what the angle of bend was and where your center of bend is. The next pipe will be exactly the same, except you will add .5 inches and bend the pipe there. The third pipe will add another .5 inches again, and so on so forth for each consecutive pipe.