Rod (unit)


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 US survey feet, equal to exactly 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.
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. In dialectal English the term lug has also been used.

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,, and ; and even as late as 1820, a House of Commons report notes lengths of,,,, and even. In Ireland, a perch was standardized at, 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, 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, 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 poetically described the measure of an acre in terms of a perch:
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, or 22 yards, or 100 links, or 4 rods. There are 10 chains or 40 rods in a furlong, and so 80 chains or 320 rods in one statute mile ; the definition of which was set by Royal surveyor John Ogilby only after the Great Fire of London.
An acre is defined as the area of 10 square chains, 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 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 drawn wrought iron linkable bar stock, 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, 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 triangulations.
The rod as a survey measure was standardized by Edmund Gunter in England in 1607 as a quarter of a chain, or long.

In ancient cultures

The perch as a lineal measure in Rome was, and in France varied from 10 feet to 22 feet. 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.

In continental Europe

Units comparable to the perch, pole or rod were used in many European countries, with names that include perche and canne, Ruthe, canna and pertica, pręt and canna. They were subdivided in many different ways, and were of many different lengths.
PlaceLocal nameLocal equivalentMetric equivalent
AachenFeldmeßruthe16 Fuß4.512N
AmsterdamRoede13 Voet3.681
Aubenas, Ardèchecanne8 pans1.985N
Baden, Grand Duchy ofRuthe10 Fuß3.0N
Basel, Canton ofRuthe16 Fuß4.864N
Bern, Canton ofRuthe10 Fuß2.932N
Barcelonacanna8 palmos1.581N
BraunschweigRuthe16 Fuß4.565N
BremenRuthe8 Ellen or 16 Fuß4.626N
BrusselsRuthe20 Fuß4.654N
Cagliari, Sardiniacanna10 palmi2.322N
Calenberg LandRuthe16 Fuß4.677N
Cassel, HessenRuthe14 Fuß4.026N
DenmarkRuthe10 Fuß3.138N
Geneva, Canton ofRuthe8 Fuß2.598N
HamburgGeestruthe16 Fuß4.583N
HamburgMarschruthe14 Fuß4.010N
HannoverRuthe16 Fuß4.671N
FrancePerche3 toises5.847N
FrancePerche toises7.145N
Genoacanna10 palmi2.5N
Jever, OldenburgRuthe20 Fuß4.377N
Mallorcacanna8 palmos1.714N
Maltacanna8 palmi2.08N
MecklenburgRuthe16 Fuß4.655N
Menorca, but not Mahóncanna1.599N
Menorca, city of Mahoncanna8 palmos1.714N
Messina, Sicilycanna8 palmi2.113N
Montauban, Tarn-et-Garonnecanne8 pans1.783N
Moroccocanna8 palmos1.714N
Naplescanna 8 palmi
Naples, Kingdom of: Apulia, Calabria, Eboli, Foggia, Lucerapercha7 palmi1.838N
Naples, Kingdom of: Capuapercha palmi1.892N
Naples, Kingdom of: Fiano, Naplespercha palmi2.014N
Naples, Kingdom of: Caggiano, Cava, Nocera, Rocce, Salernopercha palmi1.971N
Nuremberg, BavariaRuthe16 Fuß4.861N
OldenburgRuthe20 Fuß5.927N
Palermo, Sicilycanna8 palmi1.942N
ParmaPertica6 bracci3.25N
PolandPręt łokci or 10 pręcików4.320N
Prussia, RheinlandRuthe12 Fuß3.766N
RijnlandRoede12 Voet3.767
Romecanna 2N
Romecanna 2.234N
Saragozacanna2.043N
SaxonyRuthe16 Leipziger Fuß4.512N
SwedenRuthe16 Fuß4.748N
Tortosacanna1.7N
Tuscany, Grand-Duchy of canna5 bracci2.918N
Uzès, Gardcanne8 pans1.98N
Waadt, Canton ofRuthe or toise courante10 Fuß3N
WürttembergReichsruthe10 Fuß2.865N
Württembergold Ruthe16 Fuß4.583N
Venice, Republic ofPertica6 piedi2.084N
Zürich, Canton ofRuthe10 Fuß3.009N

Based on data from the following:
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.
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 by one furlong.
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, also fall measures 222 inches.

Modern use

The rod was phased out as a legal unit of measurement in the United Kingdom as part of a ten-year metrication process that began on 24 May 1965.
In the US, the rod, along with the chain, furlong, and statute mile are based on the pre-1959 values for United States customary units of linear measurement. The Mendenhall Order of 1893 defined the yard as exactly meters, with all other units of linear measurement, including the rod, based on the yard. In 1959, an international agreement, defined the yard as the fundamental unit of length in the Imperial/USCU system, defined as exactly 0.9144 metres. However, the above-noted units, when used in surveying, may retain their pre-1959 values, depending on the legislation in each state. there are plans by U.S. National Geodetic Survey and National Institute of Standards and Technology to replace the definition for the above-mentioned units by the International 1959 definition of the feet, being exactly 0.3048 meters.
Despite no longer being in widespread use, the rod is still employed in certain specialized fields. In recreational canoeing, maps measure portages in rods; typical canoes are approximately one rod long. The term is also in widespread use in the acquisition of pipeline easements, as the offers for an easement are often expressed on a "price per rod".
In the United Kingdom, the sizes of allotment gardens continue to be measured in square poles in some areas, sometimes being referred to simply as poles rather than square poles.
In Vermont, the default right-of-way width of state and town highways and trails is three rods. Rods can also be found on the older legal descriptions of tracts of land in the United States, following the "metes and bounds" method of land survey; as shown in this actual legal description of rural real estate:

Area and volume

The terms pole, perch, rod and rood have been used as units of area, and perch is also used as a unit of volume. As a unit of area, a square perch is equal to a square rod, or acre. There are 40 square perches to a rood, and 160 square perches to an acre. This unit is usually referred to as a perch or pole even though square perch and square pole were the more precise terms. Confusingly, rod was also sometimes used as a unit of area to refer to a rood.
However, in the traditional French-based system in some countries, 1 square perche is 42.21 square metres.
As of August 2013 perches and roods are used as government survey units in Jamaica. They appear on most property title documents. The perch is also in extensive use in Sri Lanka, being favored even over the rood and acre in real estate listings there. Perches were informally used as a measure in Queensland real estate until the early 21st century, mostly for historical gazetted properties in older suburbs.

Volume

A traditional unit of volume for stone and other masonry. A perch of masonry is the volume of a stone wall one perch long, high, and thick. This is equivalent to exactly.
There are two different measurements for a perch depending on the type of masonry that is being built:
  1. A dressed stone work is measured by the -cubic foot perch long, high, and thick. This is equivalent to exactly.
  2. a brick work or rubble wall made of broken stone of irregular size, shape and texture, made of undressed stone, is measured by the long, high, and thick. This is equivalent to exactly.