Laser is cutting two exact objects different lengths

Hi there all, sorry I have been quiet but my wife had surgery etc. 2024 was a hectic year. We are getting back in the saddle with our leather work hobby and our Neje Machine still has the same issues. If I may recap the following:

  1. We cannot use bidirectional because then we get a shadow or “double” on engravings.
  2. Squares/Rectangles like diary covers are longer on one side, and they become even longer the more of the board we use, like the more units of the same thing we make on the board at once.

I only now read Bernd’s suggestion of an axis calibration. How would I do that?

Does anyone have any other advice please and thank you so much in advance.