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The rod, perch, or pole (sometimes also lug) is a surveyor's tool [1] and unit of length of 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 even less common Rathborn system, also from the 17th century, is based on a 200-link chain of two rods (33 feet, 10.0584 m) length. Each rod (or perch or pole) consists of 100 links, (1.98 inches, 50.292 mm each), which are called seconds (″), ten of which make a prime ( ′ , 19.8 inches, 0.503 m).
The electrodes for electrical grounding are often called ground rods and are often made from steel with a copper clad surface – typically 1 to 2 m long and 20 millimetres (0.79 in) in diameter. These are driven vertically into the ground and bonded together with bare copper wire. [1]
1 acre is approximately 208.71 feet × 208.71 feet (a square) 4,840 square yards; 43,560 square feet; 160 perches. A perch is equal to a square rod (1 square rod is 0.00625 acre) 4 roods; A furlong by a chain (furlong 220 yards, chain 22 yards) 40 rods by 4 rods, 160 rods 2 (historically fencing was often sold in 40 rod lengths [49])
The rod is used in levelling procedures to determine elevations and is read using a level. A Philadelphia rod consists of two sliding sections graduated in hundredths of a foot. On the front of the rod the graduation increasing from zero at the bottom. On the back of the rod the graduation decrease from 13.09 ft at the bottom to 7 ft.
In many measurement systems based on former English units, the link has remained fixed at 0.66 feet, therefore 0.22 yards or 7.92 inches; it is the absolute length of the yard that has varied. A rare remaining application of the link is in the service of some surveying in the United States, which relates to the definition of the survey foot.
A rod is the same length as a perch or a pole. [24] In Old English, the term lug is also used. The length is equal to the standardized length of the ox goad used for teams of eight oxen by medieval English ploughmen. [25] The lengths of the perch (one rod unit) and chain (four rods) were standardized in 1607 by Edmund Gunter.
Surveyor's view of the levelling rod with the crosshair. This indicates a reading of 1.422 m, interpolated between the 1.420 m and 1.430 m marks. Rods come in two classes: Self-reading rods (sometimes called speaking rods). Target rods. Self-reading rods are rods that are read by the person viewing the rod through the telescope of the instrument.