NavList:

(This is my first post here. Please let me know if I run afoul of any rules or courtesies.)

I have read several articles stating that the dip of the horizon often differs by up to a few arc minutes from the Nautical Almanac's dip table. (This makes sense --refraction becomes more difficult to predict at lower altitudes and the horizon is the lowest of all.) So it seems that a person wanting precision would be well advised to measure horizon dip rather than using the table.

I have seen descriptions of prototypeinstruments for this task (e.g., the Blish prism, Admiral Davies' indirect horizon scope, a few designs by Dr. Pulfrich, and Bill Morris' improvised instrument) but none of them seems to have caught on.

I would like to measure dip myself while at sea so I am considering what type of instrument to build. I do not want to "reinvent the wheel" if someone else has a proven solution. I tested a Blish prism last summer but my device needs some refinements.

Is there a generally accepted method for dealing with horizon dip error, or an instrument generally available to measure dip? Or do most celestial navigators simply figure that any error is too minor to worry about?