Geoid wgs84.  Reference latitudes  40.0000 and  60.0000.
Tangent Latitude =  50.3601.
At  40.0000, gridsize =  8775.1372, while at  60.0000, gridsize =  8775.1372.
Difference < 1.0e-5? .. yes.
At  50.3601, gridsize =  8910.8057 
--------
Tangent Latitude =  50.0000.
At  40.0000, gridsize =  8748.3855, while at  60.0000, gridsize =  8728.9515.
Difference = 19.43397
At  50.3601, gridsize =  8874.4656 
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Geoid Clarke1866.  Reference latitudes  40.0000 and  60.0000.
Tangent Latitude =  50.3602.
At  40.0000, gridsize =  8775.0476, while at  60.0000, gridsize =  8775.0476.
Difference < 1.0e-5? .. yes.
At  50.3602, gridsize =  8910.7104 
--------
Tangent Latitude =  50.0000.
At  40.0000, gridsize =  8748.2947, while at  60.0000, gridsize =  8728.8593.
Difference = 19.43545
At  50.3602, gridsize =  8874.3685 
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Geoid sphereGrib2.  Reference latitudes  40.0000 and  60.0000.
Tangent Latitude =  50.3563.
At  40.0000, gridsize =  8782.3962, while at  60.0000, gridsize =  8782.3962.
Difference < 1.0e-5? .. yes.
At  50.3563, gridsize =  8918.5649 
--------
Tangent Latitude =  50.0000.
At  40.0000, gridsize =  8755.7531, while at  60.0000, gridsize =  8736.4547.
Difference = 19.29836
At  50.3563, gridsize =  8882.3957 
--------