Knots and (nautical) miles aren't imperial. They're useful for navigation because a nautical mile is exactly the length of a meridian arcminute, and a knot is o

Knots and (nautical) miles aren't imperial. They're useful for navigation because a nautical mile is exactly the length of a meridian arcminute, and a knot is one nautical mile per hour. Makes these units easy to use on nautical charts.