The recommended method if the position fix shows the aircraft off of the desired track and more than halfway along the leg, is as follows:
Using the diverging 10° drift lines estimate the track error or opening angle – the difference in degrees between the track required and the track made good. Then using the converging drift lines estimate the direct track to the waypoint and the angle between that track (the new required track) and the original required track. This is usually called the closing angle.
For example let’s say, on our way to CEB7, we are 7° right of the required track and the closing angle to the waypoint is about 9°. Add the track error (opening angle) and closing angle and apply the value as a correction to the original heading. If the drift was to the left of the required track the new heading will be to the right and vice versa.
For example, 7° plus 9° is 16° and drift was to the right of the original heading 146°. Therefore the heading to track directly to the destination is 130° magnetic.