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Andres with reference to your post 25^th March 14.04

As no one’s changed the title of this thread, I’m assuming that it’s OK to call a fix close enough to the body’s zenith to need to draw circles of position a ‘Zenith Fix’. 

It's probably just a language thing, but I don’t see how your software can produce a fix at 12.00 when your last piece of information was at 11.21.  A DR position based upon a fix at 11.21, yes, but a fix?  It's probably unimportant in a vessel travelling at 12 kts, but in an aeroplane travelling at 40 times that, it might be important later if you were to MPP a subsequent fix against your updated DR position, because your DR plot would have been running for 39 minutes longer than it would appear to have been if you called your 12.00 position a fix. 

I'm also wondering what the quoted error of 0.03nm at 12.00 is related to.  Is it how close your 12.00 Fix/DR position is expected to be to your actual position, or is it the difference between first and second iterations showing how quickly the solution is stabilising?  If it’s the former, that’s 61 yards, which sounds almost too good to be true.  DaveP