This is a method of assessing distance between diverging (or converging) tracks.
For every degree difference between two tracks there is a 1 nautical mile separation after 60 nautical miles of travel.
E.g. If a track is flown 5˚ Off heading, after 12 nautical miles there will be 1 nm separation.
This only works up to about 15˚ of track separation.
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