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.
In the United States surveying system, a "link" is a unit of length that is equal to 1/100th of a chain. Each link is approximately 7.92 inches long or about 0.201168 meters. This unit is primarily used in surveying and land measurement in the United States.
Surveyors often use a chain, which is comprised of 100 links, to measure distances in land surveys. The use of links and chains allows for precise measurements of land parcels, boundaries, and property lines.