Chain Conversion Chart

The international nautical mile was defined by the First International Extraordinary Hydrographic Conference, Monaco in 1929. This is the only definition in widespread current use, and is the one accepted by the International Bureau of Weights and Measures. Before 1929 different countries had different definitions, and the Soviet Union, the United Kingdom and the United States did not immediately accept the international value.

These measures were abandoned in favor of the international nautical measures in 1954.

These measures were abandoned in favor of the international nautical measures in 1970.

These units are still actively used in some countries of Latin America. Their values vary from country to country. You can find more old Spanish customary units on our historical lengths page.

Some of these units are still in use even though metric system was formally established in 1923. Before the metrication the old units were standartied to exact metric values.

A rack unit, U or RU is a unit of measure that describes the height of equipment designed to mount in a 19-inch rack or a 23-inch rack. The 19-inch (482.6 mm) or 23-inch (584.2 mm) dimension refers to the width of the equipment mounting frame in the rack including the frame; the width of the equipment that can be mounted inside the rack is less.

Grace Hopper is famous for her nanoseconds visual aid. People used to ask her why satellite communication took so long. She started handing out pieces of wire that were just under one foot long (11.80 inches) — the distance that light travels in one nanosecond. She also passed out packets of pepper, calling the individual grains of ground pepper picoseconds. She also used these aids to illustrate why computers had to be small to be fast.

In physics, natural units are physical units of measurement based only on universal physical constants. The origin of their definition comes only from properties of nature and not from any human construct.