Select Deviation from the Measurements drop down menu (or press the D key).
Place the cursor over the starting point, then press left mouse button and drag the mouse to draw a segment. Release the button to finish drawing.
The distance value in millimeters measured from one end of the segment to the straight line (either horizontal or vertical) intersecting the other end of the segment will be shown.
The second displayed value is the angle (in degrees) between the segment and the straight line intersecting one of its ends.
You can move the entire segment or one of its endings by dragging it or the cross-marks with the left mouse button pressed.
The label may also be dragged to a more convenient place if necessary.
Press Esc while drawing the deviation to delete it.