The earth turns 15 degrees in an hour
60 minutes in an hour
180 degrees N - S (90 degrees to equator)
180 degrees S - N (90 degrees from equator)
360 degrees around the equator from GM (180 degrees W/ 180 degrees E)
Each degree has 60 minutes
Each minute has 100 seconds (not 60 but a Cable of 100ths of a minute)
So
60 minutes 10 cables = 1 nm
0.6 nm at 6 knots takes 6 minutes