chain
A series of interconnected links of known length, used as a measuring device.
chain: the surveyor's 66-foot measuring standard
A chain is a rigid measuring instrument made of connected iron or steel links, each of precisely known length, joined together to form a flexible but calibrated tape. In surveying, the chain serves as the primary distance-measuring tool, establishing property boundaries, mapping terrain, and recording linear dimensions with accuracy sufficient for legal and engineering purposes.
The standard surveyor's chain in the United States is 66 feet long, divided into 100 links of 7.92 inches each. This dimension was established by Edmund Gunter in the 17th century and became the basis for the Gunter chain, which remains the legal standard. Each link is formed by a twisted wire loop soldered or welded to the adjacent link; at every tenth link, a brass tally tag is attached bearing the number of complete 10-link sections from the zero end. The total weight typically falls between 80 and 120 pounds, making two-person operation standard in fieldwork.
Variants exist for specialized purposes. The engineer's chain measures 100 feet divided into 100 links, preferred in construction and route surveying. Shorter chains of 50 feet appear in forest surveying and detail work. Metric chains (20 meters) are used in countries following SI standards, though surveying chains retain their historical lengths in many jurisdictions.
Practical limitations and wear
A chain's accuracy depends entirely on its condition. Rust, bent links, stretched wire joints, and detached tallies all introduce systematic error. Regular inspection and occasional replacement of corroded sections are necessary maintenance. Temperature changes affect the metal: a steel chain expands approximately 0.006 inches per 10-degree Fahrenheit increase, a factor surveyors must correct in precise work. Obstacles, slopes, and soft ground complicate fieldwork, requiring tension, alignment tools, and height corrections.
Though electronic distance measurement has displaced chains in professional surveying since the 1970s, chains remain legally recognized in many jurisdictions for establishing original survey records. Understanding chain measurement is essential for interpreting historical boundary descriptions, validating legacy surveys, and working with older property documents where distances are recorded in chain units rather than feet or meters.