It doesn't matter. You can choose your own datum. You can follow the plane you measure. Whether it is a round jump or a full jump, there is a reference axis. When you calibrate, you can establish coordinates on this reference axis. You can go to www.3dfamily.com Instrument Supermarket in China to learn about the information of the second and third elements. There are many articles about technologies and applications on your surface!

I hope it helps you!