The way I was shown was to make a little sketch,not to scale.Start with a horizontal line,this represents the GC track.If track is generally easterly then start point is on the left going to the right.If track is generally westerly then you start on the right and go left.Now draw in two vertical lines to represent the meridians,slightly converging if in the northern hemishere and diverging if in the southern hemishere.Work out your convergency....look at the diagram if the final angle is larger than the start angle add the convergency,if it is smaller then subtract it.Hope that makes sense.
That`s how the great god Alex W. advises to do them and certainly helps a thickie like me.Good luck.
