Hey John, you mean the long scale? That is Z in lathe parlance. Your crosslide is X. I think. Don't ask...I'm just repeating what I was told.
Tomorrow I'm going to attempt to tackle the installation of this EL400 2-axis DRO for the lathe. Then the Dorian, then the Pratt. Busy weekend planned.
Yeah, I have read the 'discussions' of different lathe axis.
The shop I worked in, back in the dark ages (1970's), did it the way I mentioned (this was before CNC arrived at that shop):
Moving the cairrage left to right (from and to the chuck) is X... and
Moving the cross slide in and out (moving across the diameter of the chuck or part) is Y.
I am sure I am gonna start a firestorm... however I suspect there are folks who do it different ways.