Alex,
I ruled that one out as both points are not on the same meridian...thinking the question was somehow related to the old INS function..I read it as asking the diff between the start latitude and the latitude at half way.
The great circle distance between the points is 597.71 nm assuming a sphere, or 600.29 nm assuming WGS84 spheriod. Using you approach I get closer to 6.78 nm for a sphere or 6.80 nm assuming a WGS84 spheriod.
May as well asked about a lambert chart instead of a polar if they were taking your approach....who knows ..
