by AC in the second post.... sorry about the confusion. I had the cable layer thing explained to me by an old geezer who had sailed on them in the '40s. I guess seriously good accuracy could be obtained.. look at the survey work carried out in the 1800s and how well some of it has stood the test of time and GPS. The Zeiss Freiburger http://landandseacollection.com/id423.html is an east german sextant...they were about $500 new before German re-unification. I carry a little Japanese yacht sextant, about half size, one of only two I have ever seen, as you say...just in case...