I've never used Anilab, I'm trying to assign a constraint or dimension that can be animated or scripted because that looked at a glance to be the simplest way of doing without having to go plugin+learning curve. I tried applying an angular dimension between the fixed datum line that the crank throw is connected to, and the throw, but it won't apply an angular dim between these elements. Animating it by rotation the red line's angle in selection info does have an advantage over possibly constraining the angular rotation because undo/redo doesn't work when you edit a constraint, it does work for sel info edits, so it could be animated manually in selinfo with ctrl z/ctrl y.
I think that you guys are right that the CS doesn't matter with constraints applied, I did that because it made more visual sense to me. The RP doesn't even have to be relocated to edit the angle in selinfo, it works with the RP anywhere in the drawing.
It can be manually animated by using the 2D selector, no bounding box, show object while dragging and just rotate the x handle approximately around the crank centre.
Bit of a disappointment that it can't be done with constraints. TC Mac and ViaCAD/Shark have an "animate" constraint. I want that one in TC PC too.