Whatever , I have a manual and cnc lathe
In my shop with just quick level job and they both cut fine, you armchair machinists make me laugh. No way a lathe bed will twist, there is a reason they are built with cast iron , unless it's over 10 feet long, average lathes you will find in home shops are very rigid
I'm of the opinion that a precision leveling job is like as not, time wasted. Most, if not all, lathes will sit near enough to straight, as to make no difference to a fellow making gun parts, and leveling the lathe so that the chip pan drains correctly is about the extent of the requirement.
If the lathe is twisted enough that barrel profiles start getting oddly tapered, per the comment above, there are far bigger twists in the bed than a precision level will fix.
You can bolt the lathe feet to a wall, for all that level matters. But then the chips will fall upon the floor, and that would not be very helpful.
If the floor is solid enough that there is no movement, then the bed can be adjusted by cranking up or down the legs. The amount of change that can be implemented this way can be measured, but most will not see the difference by eye. The two collars method of alignment is used to check the bed twist, to allow some accuracy in the parallelism of the cut.
For the most part, it is not the biggest thing a guy new to lathe work should be getting tied in knots over. The lathe bed is stiff, even the cheap little Chinese benchtop ones.
And, it is worth noting, nobody around here (OK, for the most part, as I can think of one, at least) is like to be making parts that need to meet specifications off a blueprint from NASA.
A lathe plonked onto the floor, with the legs adjusted to sit evenly, is going to do far better work than many new users will be led to believe.
But not until the guy running it has put his time in and learned how to use it.
Aligned, trumps level.
A point too ponder. How much time do y'all figure that low paid Chinese labor, put in to precision leveling the castings on the grinder they ground the ways of the lathe on? How long did they let the castings stress relieve in the yard before they machined them?
Precision leveling is predicated on the assumption that the bed was carefully leveled and made to the same or higher precision than the leveling process that is being followed. Think on that, and how likely it is to have happened in the making of a budget Chinese lathe, eh.
Set it up, adjust as required to get a reasonably parallel cut, and go to town on it. You can learn
about running a lathe by reading about it or talking about it, but you will only learn how to do it, by doing it!
Cheers
Trev