These would be the points corresponding to 0, 90, 180, and 270 degrees. Drawing a complete gcode circle involves not just coordinated motion but reversal of direction at each of the 4 quadrant points. Circular interpolation is quite a bit more demanding on your machine as two axes have to be precisely coordinated. Other than the fairly exotic ability to follow a “NURBS” path, most g-code controllers only support two kinds of motion: linear and circular motion. Having just finished discussing linear interpolation, or motion in a straight line, we next come to circular interpolation, which is motion along a circular arc. Quick G-Code Arc Tutorial Circular Interpolation is Motion Along a Circular Arc