NavList:

As you get further into your project, I will be interested in your assessment as to the point where additional significant digits get lost in the mathematical noise associated with living on a non-spherical earth...and even more, a non-spherical earth with a bumpy surface.  At some point, additional significant digits might even lead one astray through a false sense of precision.

Bob

"It lacks now three minutes of the half-hour," shouted the captain, as he gave me the longitude and the time. I admired the businesslike air of the Olympia; but I have the feeling still that the captain was just a little too precise in his reckoning. That may be all well enough, however, where there is plenty of sea-room. But over-confidence, I believe, was the cause of the disaster to the liner Atlantic, and many more like her. The captain knew too well where he was."

Joshua Slocum, Sailing Alone Around the World