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The rod or perch or pole is a surveyors tool〔 and unit of length equal to 5 yards, 16 feet or of a statute mile and one-fourth of a surveyor's chain. The rod is useful as a unit of length because whole number multiples of it can equal one acre of square measure. The 'perfect acre'〔 is a rectangular area of 43,560 square feet, bounded by sides 660 feet by 66 feet long (660 ft long × 66 ft wide), or 220 yards by 22 yards long (220 yd/ long × 22 yd wide), or 40 rods by 4 rods long. Thus, an acre is 160 square rods. Since the adoption of the international yard on 1 July 1959, the rod has been equal to exactly 5.0292 meters. A rod is the same length as a ''perch'', also sometimes called a pole which measure using cordage〔 or wood, slightly antedated the use of both rods and surveyors chains, made of more dimensionally regular materials. The measure also has a relationship to the military pike of about the same size and both measures〔 date from the sixteenth century,〔 when that weapon was still utilized in national armies. The tool, normally configured as a metal rod with eye-ends (loops that could be hooked together), was used commonly until quite recently, when it was supplanted by electronic tools such as surveyor lasers (Lidar) and optical target devices for surveying lands. Surveyors rods and chains are still utilized in rough terrains with heavy overgrowth where laser or other optical measurements are difficult or impossible. In old English, the term ''lug'' is also used.〔〔 ==History== Until English King Henry VIII seized the lands of the Roman Catholic Church in 1536,〔name="Connections">〕 land measures as we now know them were essentially unknown.〔 Instead a narrative system of landmarks and lists was used. Henry wanted to raise even more funds for his wars than he'd seized directly from church property (he'd also assumed the debts of Monasteries〔), and as James Burke writes and quotes in the book ''Connections'': the English Monk Richard Benese ''"produced a book on how to survey land using the simple tools of the time, a rod with cord carrying knots at certain intervals, waxed and resined against wet weather. Benese who poetically described the measure of an Acre in terms of a perch:〔''Connections'', pbk. p.263〕 The practice of using surveyor's chains, and perch length rods made into a detachable stiff chain came about a century later when iron was a more plentiful and common material. A chain is a larger unit of length measuring 66 feet (20.1168 meters), or 22 yards, or 100 links,〔The Cassell English Dictionary, London 1990, p. 214, ISBN 0-304-34003-0〕 or 4 rods (20.1168 meters). There are 10 chains or 40 rods in a furlong (eighth-mile), and so 80 chains or 320 rods in one statute mile (1760 yards, 1609.344 m, 1.609344 km); the definition of which was set by Royal surveyor (called the 'sworn viewer'〔"Connections", pbk. pp265〕) John Ogilby only after the Great Fire of London (1666). An acre is defined as the area of 10 square chains (that is, an area of one chain by one furlong), and derives from the shapes of new-tech plows〔Connections, pbk. pp63〕 and the desire to quickly survey seized church lands into a quantity of squares for quick sales〔 by Henry VIII's agents; buyers simply wanted to know what they were buying whereas Henry was raising cash for wars against Scotland and France.〔 Consequently, the surveyor's chain and surveyor rods or poles (the perch) have been used for several centuries in Britain and in many other countries influenced by British practices such as North America and Australia. By the time of the industrial revolution and the quickening of land sales, canal and railway surveys, et al. Surveyor Rods such as used by George Washington were generally made of dimensionally stable metal—semi-flexible pinky-finger-tip-thin drawn wrought iron linkable bar stock (not steel), such that the four folded elements of a chain were easily transportable through brush and branches when carried by a single man of a surveyor's crew. With a direct ratio to the length of a surveyor's chain and the sides of both an acre and a square (mile), they were common tools used by surveyors, if only to lay out a known plottable baseline in rough terrain thereafter serving as the reference line for instrumental (theodolite) triangulations. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Rod (unit)」の詳細全文を読む スポンサード リンク
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