Coordinate Systems / Scales > Align Horizontally, Point - Point (Manage Menu)

This command aligns the rotation of the active window's coordinate system to a line defined by two points so that that line is being displayed horizontally.

The first point through which the line should run can be entered by clicking the mouse anywhere in the drawing.

The second point through which the line should run can be entered by clicking the mouse anywhere in the drawing.

After the line has been entered, the coordinate system's rotation will be aligned to it.