Simple and reliable XY square test

Are the X- and Y-axes of your printer perpendicular? This simple test reveals the answer without precision measurement equipment.

While making a large object consisting of several parts with tight tolerances, I learned that the X- and Y-axes of my Creality CR-20 PRO were not exactly perpendicular. To reveal the magnitude of error, I designed this tool. When printed and placed on a flat surface as the photos show, the angle between the L and R parts is twice the deviation of the angle between X- and Y-axes from 90 degrees.

The triangles can be printed together (xy90.stl) or separately (L and R). If you print the parts separately, make sure that the 90 degree angles point to opposite corners. Slice the triangles on the printer bed so that sides labeled X and Y are parallel to X- and Y-axes of the printer. This makes it easier to decide the direction of correction. If the gap between the triangles widens downwards, as in photo "before", Y-axis should be turned clockwise or X-axis sh