Hi Nigel,

> Use apparent intersections

This affects intersection object snap. An "apparent intersection" is when 2 curves visually cross over each other in one of the ortho Top/Front/Right views.

When this option is enabled, you can get intersections in those viewports at those visually intersecting spots even though the actual 3D curves do not intersect in 3D space.

Here's an example - here I've got 2 lines which are on different z levels, in the 3D view they look like this:



But those same lines in the Top view look like this:



When "Use apparent intersections" is enabled, that allows you to go in the top view and get an intersection snap at this point here:



The actual point that is used will be on one of those curves, the one used will be the one that the mouse is closest to.

So for instance with the mouse in this spot close to this line, it will give this snap point:



And if you move the mouse over slightly so it is closer to the other line, it will make the snap point on that other curve like this instead:



You can disable this option if you don't want to get these kinds of snaps and only get intersection snap points where the curves actually touch each other in full 3D space.

Some info on the other option in a minute...

- Michael