page_title: Rod (unit)
section_title: In Britain
hierarchical_section_title: Rod (unit) / History / In Britain
caption_attribution_description: English: Holyrood Palace and Abbey Source: http://www.wyrdlight.com Author: Antony McCallum
context_page_description: The rod or perch or pole is a surveyor's tool and unit of length of various historical definitions, often between 3 and 8 meters. In modern US customary units it is defined as ​16 ¹⁄₂ US survey feet, equal to exactly ​¹⁄₃₂₀ of a surveyor's mile, or a quarter of a surveyor's chain, and is approximately 5.0292 meters. The rod is useful as a unit of length because whole number multiples of it can form one acre of square measure. The 'perfect acre' is a rectangular area of 43,560 square feet, bounded by sides 660 feet long and 66 feet wide or, equivalently, 40 rods and 4 rods. An acre is therefore 160 square rods or 10 square chains.
  The name perch derives from the Ancient Roman unit, the pertica.
  The measure also has a relationship to the military pike of about the same size. Both measures date from the sixteenth century, when the pike was still utilized in national armies. The tool has largely been supplanted by electronic tools such as surveyor lasers and optical target devices for surveying lands. Surveyors rods and chains are still used in rough terrains with heavy overgrowth where laser or other optical measurements are difficult or impossible.
context_section_description: In England, the rod or perch was first defined in law by the Composition of Yards and Perches, one of the statutes of uncertain date from the late 13th to early 14th centuries: tres pedes faciunt ulnam, quinque ulne & dimidia faciunt perticam (three feet make a yard, five and a half yards make a perch).
  The length of the chain was standardized in 1620 by Edmund Gunter at exactly four rods. Fields were measured in acres, which were one chain (four rods) by one furlong (in the United Kingdom, ten chains).
  Bars of metal one rod long were used as standards of length when surveying land. The rod was still in use as a common unit of measurement in the mid-19th century, when Henry David Thoreau used it frequently when describing distances in his work, Walden.
  In traditional Scottish units, a Scottish rood (ruid in Lowland Scots, ròd in Scottish Gaelic), also fall measures 222 inches.
caption: Holyrood, Edinburgh
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