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The line perpendicular to segment AB through its midpoint.

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There are two ways to hand it the segment to bisect, and you use one or the other: wire a ready-made Segment, or give it the two endpoints as Point A and Point B. If a segment is wired, it takes priority and the two point inputs are ignored; with nothing on Segment, the node falls back to A and B.

• Segment (curve): a segment (or any geometry containing straight segments) whose endpoints set the segment to bisect. Built this way, the bisector tracks those endpoints as they move. Every straight segment wired in yields its own bisector.
• Point A (point) / Point B (point): the fallback, used only when no segment is wired: the bisector crosses the midpoint of A->B at a right angle. Point lists pair index-for-index, one line per pair.

• Line (curve): the perpendicular bisector line.

Every point on this line is the same distance from both ends of the segment, which is what makes it the classical way to find a center. Cross the bisectors of two chords and you have the center of the circle they belong to.

It is also the axis to reflect across when you want two points to swap places, so it feeds Mirror when the symmetry comes from the geometry rather than from an axis you drew.

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• In the modeling view: Line: Perpendicular Bisector - construct the same perpendicular bisector directly on the canvas.