Question Polar stereographic chart

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hello whiteknight,

following might be an answer to your nav problem.
formulae & elaboration:
(1) delta R(earth converg)=delta g(longitude)xsinlm(mean latitude)
so: 20°=delta g x sin60°

for info: a quick means to find sin & cos values

0 1 2 3 4
0 1 1.41 1.73 2 = square root
0 0.5 0.7 0.866 1 = divided by 2
0° 30° 45° 60° 90°=sin values(corresponding numbers abv)
90° 60° 45° 30° 0° =cos values(reverse order)



so again:20°=delta g x 0.866 with delta g=23.09°=23°[1]

(2)greek delta letter(pseudo givry correction)= angle between chart straight line & ortho line)= 0.5xdelta gx(1-sinlm) for stereo polaire chart.
so: greek delta=0.5x23°x(1-0.866)=1.54°[2]

(3)loxo distAB=delta gx coslm=23°xcos60°=23°x0.5=11.5°x60=690nm. corresponding ortho dist= 688nm[3] (formula ortho dist: cosM=sinlatAxsinlatB + coslatAxcoslatBxcosdelta g

(4) f(la fleche, in french)=max offset dist between chart straight line & ortho line= greek delta x ortho distAB(nm)/230

so finally putting [2]&[3]in this formula gives: f=1.54x688nm/230=4.6nm so 4nm offset seems a reasonable answer.

note: somebody suggested that for a stereo polaire chart , angle between chart meridians & delta g(longitude) are the same & this is correct as n(constant of the cone)= 1 for stereo polaire chart: delta alfa=nxdelta g with n=1.

i stop here before getting a real headache.