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The difference is in the factor A used in both examples.

For WGS84 this is A = 6378137 / 1852 = 3443.9185
in the second example this is A = 3437.7468

The term inside the logarithm is the same for both examples.

/Eddie

George Huxtable wrote:
> The plot thickens-
> 
> Andres calculates, from the expression he gives in [7784]
> 
> WGS84
> 
> a = 6378137 [m] = = 6378137/1852 [nm]
> 
> f = 1.0/298.257223563
> 
>  The result is:
> 
> MP( 45.000000 ) = 3019.058271357112100000
> 
> The expression Andres quoted used eccentricity (epsilon) rather than the 
> flattening f that he tells us is f = 1.0/298.257223563 for WGS84. However, 
> we can deduce one from the other using the expression given in Meeus, in 
> which
> eccentricity = square root of ((2 * f)  - (f * f)) for which I have taken 
> the result to be 0.08181919, exactly in keeping with Earle's figure.
> 
> ===========================
> 
> On the other hand, I have tried to do exactly the same thing with my pocket 
> calculator and with the following values, taken from Earle-
> E= 0.08181919
> A = 3437.7468, the Earth's equatorial radius in geodetic miles.
> Latitude L= 45
> 
> and here's a transcription of the equation I've used, now corrected, which 
> runs on a 20-year-old Casio programmable calculator-
> M=A*LN(TAN(45+.5*ABSL)*((1-E*SINABSL)/(1+E*SINABSL))^(E/2))
> 
> and that gives me M(45�) = 3013.648, which conforms with Bowditch, and not 
> (quite) with Andres..
> 
> Why do Andres and I differ (slightly), and why do I agree with Bowditch, 
> when Andres and I are trying to calculate the same thing with the same 
> quantities, using what appears to be the same expression?
> 
> You can see that I've rejoined the nit-picking purists, as my natural home.
> 
> George.
> 
> contact George Huxtable, at  george@hux.me.uk
> or at +44 1865 820222 (from UK, 01865 820222)
> or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
> 
> 
> 
> > 

-- 
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Eddie C. Dost           Rue de la Chapelle 51      phone +32 87 788817
                         B-4850 Moresnet            fax   +32 87 788818
ecd@brainaid.de         Belgium                    cell  +49 172 9312808


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