This is the International nautical mile; the UK nautical mile is 1.85318 km. We have adopted the symbol n. mile to avoid confusion with nanometres (nm).

A foot is the unit of length in the old British system of units.

This has 8.5 ppm uncertainty. When a standard temperature of 290 K is used:

The Earth's shape is an oblate spheroid with an equatorial bulge caused by its rotation. The figure above is the equatorial radius or semi-major axis. The polar radius, or semi-minor axis is 6356.775 km.

Some SI prefixes commonly used in radar are:

Reference source: The McGraw-Hill Dictionary of Science and Technical Terms, 4th edn, Ed. S. P. Parker, McGraw-Hill, New York, 1989.