As I understand the 440 it only supports the harmonic 4th axis
so for any mill other than the 440 you have 2 options for 4th axis, Duality and a normal 4th axis. on the 440 you have only the duality (ie harmonic) axis
that's the way I ready it anyways so if you're adding a 4th axis that is not a duality then you would still use the harmonic axis setting and not scale.
