Perpendicular snaps to the point on an object that forms a normal, or perpendicular alignment, with another object or with an imaginary extension of that object. You can use the Perpendicular object snap with arcs, circles, ellipses, lines, polylines, or splines.
When you use the Perpendicular object snap to specify the first point of a line, xline, or circle, you construct a line or circle that is perpendicular to an object you select. When you use the Perpendicular object snap to specify the second point of a line or circle, AutoCAD LT snaps to a point that creates a normal from that object to the first point selected.
You can use a perpendicular snap with arcs and circles that are part of a block only if the block has been uniformly scaled and the object's thickness direction is parallel to the current UCS. You may not be able to construct perpendicular lines between all objects.