Edit Bar controls: none.
This tool allows you to align the picked point orthogonally (that is perpendicular) to the previously entered points.
For example, if you are drawing a series of connected lines using Draw>Multiple Lines and Arcs from the menu, using this tool can ensure that the next line drawn is at 90 degrees to the previous line, even if the first line is not aligned with one of the axes.
This lock mode remains on until you select another lock mode.
Related topics: Snap Modes and Lock Modifiers