Better calibration model

Larger than the traditional calibration cube, reducing the effects of measuring errors, along with chamfers on all edges to avoid issues with elephants foot and over-extrusion. You can both do internal and external measurements, to determine accuracy. External measurements are 100mm on X, Y, and Z axis, while internal is 60mm. All solid parts are 20mm on the short side. Test for squareness of your prints on the vertical parts