X and Y calibration square

thingiverse

You can use this handy tool to verify that your X axis moves perfectly perpendicularly to your Y axis. This is particularly useful for home-built printers, where accuracy matters most. After printing, measure the distance from each diagonal corner of the square. If both measurements are identical, your printer's axes are properly aligned. However, if there is a noticeable difference, it indicates that your printer's axes are not perpendicular to each other.