Wouter WHY do you always assume that my replys are pertinent only to you (which they aren't) I am not critisizing you, I am only answering to the "general forum"
By the way, for 10 years I did work as a surveyer AT sea (as you call it) doing harbour and channel surveying as well as mining survey where it is one of the most difficult and critical areas of establishing PRECISE (more than accurate) datum points, so I would appreciate it if MY qualifications were not called into doudt thank you. Why do you seem so aggressive? or is it just my imagination? Chill out and enjoy life as it passes you, don't always fight with it, we will all be a long time dead.