Late to this discussion. However I recently bought an Ender 3 Pro and calibration of all 3 axes and the extruder itself is very easy. You can print an XYZ cube, and then when cool, measure each dimension being sure to avoid elephants foot at the base. It is then a simple matter for each axis to calculate the ratio of expected dimension divided by achieved dimension, and multiply the steps per mm in the menu by that figure. Do this for all 3 axes and then save the results from the on-screen menu. No need to go into Cura or any other splicer. I have printed several 20mm XYZ cubes and after correcting the steps per mm, all sides are between 20.00 and 20.02mm, which about as accurate as a 3d print can be measured. There are plenty of YouTube videos showing the process.