Perfect
You know what you could do.. Is add another (4th) zoom level with magnification 2x (or 5x, 10x) the sextant one. If one centres (vertical and horizontal) the object of observation.. and then turns on the more powerful magnification level, you should get an offset from the centre point that is measurable.
This offset would be the added/subtracted to the original reading to get a more accurate one. Something similar to how a vernier (and sextant) works on the smaller scales.
Now if the sky/star system is this accurate wrt to the map... one should be able to land a torp down Winstons' bath plug.