The rod, perch, or pole (sometimes also lug) is a surveyor's tool and a unit of length with various historical definitions. In British imperial and US customary units, it is defined as 16+1⁄2 feet, equal to exactly 1⁄320 of a mile, or 5+1⁄2 yards (a quarter of a surveyor's chain), and is exactly 5.0292 meters. The rod is useful as a unit of length because integer multiples of it can form one acre of square measure (area). The 'perfect acre' is a rectangular area of 43,560 square feet, bounded by sides 660 feet (a furlong) long and 66 feet (a chain) wide (220 yards by 22 yards) or, equivalently, 40 rods by 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 with 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 been supplanted, first by steel tapes and later by electronic tools such as surveyor lasers and optical target devices for surveying lands. In dialectal English, the term lug has also been used, although the Oxford English Dictionary states that this unit, while usually of 16+1⁄2 feet, may also be of 15, 18, 20, or 21 feet.
History
In England, the perch was officially discouraged in favour of the rod as early as the 15th century; however, local customs maintained its use. In the 13th century, perches were variously recorded in lengths of 18 feet (5.49 m), 20 feet (6.1 m), 22 feet (6.71 m) and 24 feet (7.32 m); and even as late as 1820, a House of Commons report notes lengths of 16+1⁄2 feet (5.03 m), 18 feet (5.49 m), 21 feet (6.4 m), 24 feet (7.32 m), and even 25 feet (7.62 m). In Ireland, a perch was standardized at 21 feet (6.4 m), making an Irish chain, furlong and mile proportionately longer by 27.27% than the "standard" English measure. Until English King Henry VIII seized the lands of the Roman Catholic Church in 1536, modern land measures 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 had seized directly from church property (he had also assumed the debts of the monasteries), and as James Burke writes and quotes in the book Connections that 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 described the measure of an acre in terms of a perch:
an acre bothe of woodlande, also of fyldlande [heath] is always forty perches in length, and four perches in breadth, though an acre of woodlande be more in quantitie [value, i.e. was more valued commercially] than an acre of fyldelande 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 m), or 22 yards, or 100 links, 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 legally set in 1593 and popularized by Royal surveyor (called the 'sworn viewer') 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 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 with surveys for land sales, canals and railways increasing, surveyor rods such as those used by George Washington were generally made of dimensionally stable metal—semi-flexible drawn wrought iron linkable bar stock (not steel) so 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. The rod as a survey measure was standardized by Edmund Gunter in England in 1607 as a quarter of a chain (of 66 feet (20.12 m)), or 16+1⁄2 feet (5.03 m) long.
In ancient cultures The perch (pertica) as a lineal measure in Rome (also decempeda) was 10 Roman feet (2.96 metres), and in France varied from 10 feet (perche romanie) to 22 feet (perche d'arpent—apparently 1⁄10 of "the range of an arrow"—about 220 ft (67 m)). To confuse matters further, by ancient Roman definition, an arpent equalled 120 Roman feet. The related unit of square measure was the scrupulum or decempeda quadrata, equivalent to about 8.76 m2 (94.3 sq ft).
In continental Europe
Units comparable to the perch, pole or rod were used in many European countries, with names that include French: perche and canne, German: Ruthe, Italian: canna and pertica, Polish: pręt and Spanish: canna. They were subdivided in many different ways, and were of many different lengths.
In Britain and Ireland
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