Due to floating-point math, the point cannot be put on the very end of the arc or else it’s liable to fall off, (& that’s going to play merry havok with your patterns for sure.) So it’s best practice to make your arcs start & end at least a little beyond where they need to be. eg, have a first angle of -1, or 0-1 if the zero is important to your tracking of what you’re working with. (Personally, I’d go with -3, just for extra wiggle-room.)

.1 mm is not enough accuracy? That’s .04 or 4/100ths of an inch.

If if you need that kind of accuracy do like @Pneumarian suggested and make the arc bigger, and then using the Point - Intersect Curve and Axis, create your points A1 and A2 at 0 and 90 degs.

BTW… doing it this wayalso makes adding the lines A_A1 and A_A2 moot as the lengths are added as a variable when you add the points A1 and A2.

Actually for what ever reason… which I think we’ve been over this before - RT hardcoded it so that if you try to put the point at the start (length 0) or end (length of arc)… it puts it 1mm away? I have no idea why he did this as this has nothing to do with the fuzzy math.