Another thread necromanced into the living.
3 minutes stems from 100 yards in a nautical mile. Or movement of 1 knot in 1/20th of an hour. As 1 nautical mile is actually 2025.something yards. So close to 2000 yards for an easy measure. And 3 minutes would be close to the time it takes 1 knot to move 100 yards on graphpaper, so 1/20th of a nautical mile. It's 1.2 % inaccurate, but good enough for Government work, as they say.
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