A chain is a unit of length used in some older systems of measurement, particularly in surveying and land measurement. In the United States, one chain is equal to 66 feet or 22 yards. Internationally, it's defined as exactly 20.1168 meters.
Chains were historically used for measuring large plots of land and for surveying purposes, often in agriculture and real estate. However, the use of the chain as a standard unit of measurement has largely been replaced by the more modern and standardized metric and imperial systems, which use units like meters, feet, and yards.
The term "chain" comes from the practice of physically measuring land using a chain made of linked metal bars or wire. Each chain was typically 66 feet long, and surveyors would lay out chains end to end to measure distances across large areas. Today, modern surveying equipment such as electronic distance measuring devices (EDMs) and GPS technology have largely replaced the use of physical chains in land surveying.
The "cubit" is an ancient unit of measurement for length that was historically used in various cultures, including ancient Egypt, Mesopotamia, and the Hebrew Bible. It was typically based on the length of a person's forearm from the elbow to the tip of the middle finger. As a result, the actual length of a cubit could vary from region to region and even from person to person.
In the United Kingdom and other parts of the world where the British imperial system was historically used, a cubit was typically defined as roughly 18 inches or about 45.72 centimeters. This is often referred to as the "British cubit."
However, it's important to note that the cubit is an ancient and non-standardized unit of measurement that has largely fallen out of use in modern times. Today, standardized units such as feet, meters, and inches are used for precise measurements, and the cubit is primarily of historical and cultural interest.