A femtometer (fm), also known as a fermi, is an extremely tiny unit of measurement used to express even smaller distances than a picometer. It is equal to one quadrillionth of a meter, which is 0.000000000000001 meters or 1 × 10^-15 meters. The prefix "femto" denotes a factor of 10^-15 in the International System of Units (SI).
Femtometers are typically used in the field of nuclear physics and particle physics to describe the sizes and distances involved in atomic nuclei and subatomic particles. The nucleus of an atom, for example, is on the order of a few femtometers in diameter. In high-energy physics experiments and discussions about fundamental particles like protons, neutrons, and quarks, femtometers are a relevant unit of measurement due to the incredibly small scales involved.
There isn't a widely accepted international standard for a "nautical league." The nautical mile (nmi) is the more common and internationally recognized unit of measurement for distances at sea. A nautical mile is approximately equal to one minute of latitude along a meridian, and it is used worldwide for maritime and aviation navigation.
In some regions, historical or localized variations of the league may have been used in the past, but these are not part of the modern international system of measurement. It's important to note that such variations can differ by country and even within different historical periods.
For precise and internationally recognized measurements in maritime and aviation contexts, the nautical mile is the preferred unit of distance. One nautical mile is equal to approximately 1.852 kilometers or 1.15078 statute miles (land miles).