NavList:

In [NavList 7769] all values for a, are in nautical miles.

a: Semi-major axis = equatorial radius. Is the radius of curvature in a meridian plane at the equator.

Using the formula arc = angle(rad)* a, we have a =  360*60/(2π) [nm]

But also a =  360*60/(2π) [geodetic miles]

The radius is 21600 sexagesimal arcminutes, and geodetic minutes.

Average minute of geodetic latitude is:

I have attached the meridional parts table that appears in the “Tratado de Navegación - Mendoza Rios Tomo II” in 1787

I have compared its values, and conclude that uses the spherical model of the Earth.

The update from the spherical model to al ellipsoidal one must be done using a model like WGS84, WGS72, NAD83 or EUROPE1950. If this would have be done by Bowdith, no error of interpretation or concept will arise.

Andrés Ruiz

Navigational Algorithms

http://www.geocities.com/andresruizgonzalez