I originally ordered the 3 axes system, but decided to upgrade- I returned the original display and JT sent me the 4 axes display and 4th scale for the mill head. The mill head scale went on in less than 10 minutes, as the mounting holes and drive bracket are already in place. When I first got the machine I put my display in the " default" location on the front of the Z axis CNC motor shield. This was too close for my liking, so I moved it to the end of the mill head support arm. Unfortunately, I got tired of looking to the right to read the scale. I now have it mounted on the front of the mill cover- its easy to read and reach the buttons, but not right in my face. The system has a lot of functions I haven't tried yet, but one is the addition of 2 axes. I think I can add the travel of the quill to the travel of the mill head and have it display as a single dimension, and give me a much larger and accurate range on my mill.