I guess what I don’t understand is: length is relative to what?

Position is every vertex’s [xyz]

Multiple does something that probably means “ignore the X value”

And then length measures from the position of each vertex to what exactly? It’s not intuitive to me.

Verts with a length less than 1 are selected and separated from the rest of the geometry and then the selected verts are the only ones used. I assume this is somehow faster than deleting the geometry. If so, why?

Sure! since you dont care about any changes on the x axis, only the distance from it, moving along the x axis should have no effect on the outcome. So if we take the position data and flatten it on the x axis (by scaling the position vector to zero on the x axis, but leaving the y and z axes at 1) then we can compare the length of this flattened vector. any point that is more than 1 meter away from the origin (after scaling) is within 1 meter of the x axis, along it’s entire length.

I think so. If you have a point [x,y,z] and another point [x,y,z] like [0,0,0] then you have a vector between the 2 points and the vector has a length.

now, if you had a point that is at the origin: location = [0,0,0] that point is definitely on the x axis, so it’s distance to the axis is 0. if we take that same point and move it 100 meters away, along the x axis: location = 100,0,0, but it is still on the x axis.

What if we move both of those points up 1 meter? [0,0,1] and [100,0,1] are now both 1 meter away from the x axis.

so no matter what the x value, it doesn’t change the distance from the x axis.

Maybe this is more understandable by answering the first question first ( solutions should go to @SterlingRoth anyway because i just changes it a bit ):

And if you want the whole x-axis as refering object then the x coordinate is of no interest in the length because you would measure the distance to the x-axis (length) for every point at that x position… so just multiplying this with 0… or just measure to y and z. ( mult with 1 → no change)…

The problem is solved. I’m just too stupid to understand how the solution actually works, which means I’m going to come crawling back here begging for help in the future for things that probably have a similar solution but I’m unaware of how to solve it myself.