Hi Sean, so a couple of the things you're worried about there are just display artifacts that will happen when under extreme zoom.

Basically if you zoom in a whole lot you'll start to see some evidence of the limited precision of floating point mathematics on the computer. The computer uses a number representation that has to fit in a limited amount of memory and that causes little rounding errors for every bit of arithmetic. But they're very small and so it's just a normal part of how things work on computer CAD.

The deviation that you're worried about in the first part of your video is about 0.0000019 units, which is small enough to just not really worry about. Not that it's bad for things to be exactly aligned but many things like intersection calculations are calculated by a refinement process that adds more detail to the intersection curves until they are within 0.001 units of the ideal answer. That's a different thing than arithmetic precision but it's also another thing that means that very small deviations on the order of what you're worried about are just normal things.

The second thing when you're asking "what's this stuff" is where the shaded surface display is separating off a bit from the curve display - that's also just a display artifact under high zoom, the shaded display part of video cards tends to use a smaller sized floating point number even yet and so tends to be a little more hit by precision issues and also the curve display is done fairly differently than the shaded surface part, curves are broken down dynamically on every draw to within a fraction of a pixel of the true curve so those display very accurately but it's too much work to do this for the shaded surface and so the surfaces have a triangle mesh formed for them just once using world space angle metrics and then that's what is still used to draw even under high zoom. So it's just another normal thing that they will separate under high zoom.

A lot of these things just boil down to shortcuts that have to be taken in order to make things work quickly and without taking up gigantic amounts of memory, if all operations worked to tighter than 0.0000019 and the display tried to draw even extreme zoom at super accuracy everything would run like molasses.

I'll try to take a look at your little line floating out in space, that might be something to actually worry about.

- Michael