This method for keeping a boat on track as she moves down a safe line from a known charted object is moderately accurate. The trouble is that deciding which way to turn when the reversed bearing becomes larger or smaller than the ideal is the sort of brain-teaser nobody but a maths professor really wants. The solution is to hold the compass steady on the desired bearing, then note whether the object moves left or right of it. If it drifts out to the right, it will be obvious that to bring the object back into line, you must steer to port. Try it. It works like a charm.