Selects a point perpendicular to an entity
The Perpendicular snap is used with the Copy and Move commands to specify a point perpendicular to the previously selected entity.
The selected entity can be a circle, line, or rectangle. The selected entity can be divided at the point where the imaginary line would intersect it, depending on the Options setting.
Both green lines are perpendicular
In the figure below, (S) is the starting point of the green line, which was drawn to be perpendicular to the rectangle. The line was drawn to be at 90° to the imaginary extension of the line.
The green line was drawn from (S) to be perpendicular to the box