Hi Adih, Usually the PWB fabricator will calculate the different lengths for the flex arms, to create the "hump". The designer sends in the gerber and print, with the gerber files all the same length, but indicates on the print that the part is to be manufactured as a bookbinder rigid flex. Once, I did see a customer do all of the calculations themselves. They hired an intern for the summer, and that was his summer project! But I have only seen it that one time; it was quite the project and the intern really threw himelf/herself into it!