I made this to see if my printer bed was flat. This is 0.2mm thick with 0.4mm wide lines. This thickness was the lowest I wanted to test for my Da Vinci 1.0. The width of the lines was the lowest that the slicing software would detect reliably (it takes a lot longer for the slicer to solve this than you would think, 8 minutes plus for me).

It can take an hour or so to print, but it does look cool once done, almost like a tunnel going off into infinity (thus the name).

I was able to determine my print bed is slightly convex, or maybe the printer head dips down in the center due to weak support. Either way it also shows if your bed is level with the print head.

This test is for a 200mm X 200mm bed. I only made it 195mm X 195mm because the slicer would not accept it at 200mm on the dot.

4.5 Degrees center to center (C.T.C.) between each radial line. 10mm C.T.C. of each horizontal or vertical line (except for the innermost lines which are 14.6mm C.T.C. because having 10mm spacing from the outside in leaves an odd number when starting with 195mm plus the 0.4mm line thickness...

I could be willing to modify this if asked. But just take my SolidWorks file instead.