HOW DO I MAKE MY MACHINE SQUARE?

I use a standard large "L" square used in construction. I run gantry up and down with the bit along one side of the square to make the square aligned with the x-axis. I then run the bit along the other edge and if I see space from the edge of the bit to the square, I adjust the gantry square by loosening and tightening the eye bolts that hold the chain at the ends of the table. Repeat as necessary to get the desired square. Additional Information: