Hi Burr, just another note:

> Is there something about that last point I picked that
> controlled this? Is there anything in this method that
> controls the "up" of my path or is it automated?

It's nothing about that last point - the twisting is due to the way the rail path travels around in 3D instead of being planar.

When a sweep profile curve is following a 3D path, there is a kind of gradual twist that happens to it as it follows up and down humps, etc... - it's something that helps each new positioned curve to be as minimally different from the previous one as possible.

If it didn't do that, it would tend to swing around more suddenly at some spots as it changed in orientation.

The "flat" twist option does it differently and only rotates around the world z axis. But there you will see the kind of sudden large jumping for paths that have a tangent that approaches that z axis direction.

- Michael