So DUMB we are!
Did you ever wonder what was the purpose of the dashed, zoom sensitive, lines on the borders of the map?
We have it right in the front of our noses and never got it....
So.....NO!?....Really?!.....Meridiens and Parallels of course!
You don't believe me? Just go to the cross point between the AN26-AN21's limit and the Greenwich meridien. Yes, you are on the 60 N and 0 W point.
You can find another references as well : vetical limit between AM and AN grids on their north part fit the 5 W....and so on.
So now you can draw your own parallel and meridien lines everywhere in the world!...Nice, isn't it...
And with the most precision due to the level of zoom you choose.
Another tip : After having set a course heading, wait a little to be sure you are on the straight line and then hit rudder amidship. This should help the helmsman to stay alert during the course.