Units of Measurement. Manual of Instructions for the Survey of the Public Lands of the United States |
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p. 18 Chapter II Methods of Survey The methods described in this chapter comprise the specifications for determining the length and direction of lines. DISTANCE MEASUREMENT Units 2-1. The law prescribes the chain as the unit of linear measure for the survey of the public lands. All returns of measurements in the rectangular system are made in the true horizontal distance in miles, chains, and links. (Exceptions are special requirements for measurement in feet in townsite surveys, chapter VII, and mineral surveys, chapter X.)
The chain unit, devised in the seventeenth century by Edmund Gunter, an English astronomer, is so designed that 10 square chains are equivalent to one acre. In the English colonial area of the United States the boundaries of land were usually measured in the chain unit, but lengths of lines were frequently expressed in poles. One pole is equal to 25 links, and four poles equal one chain. The field notes of some early rectangular surveys in the southern States show the distance in "perches," equivalent to poles. The term now commonly used for the same distance is the rod. Land grants by the French crown were made in arpents. The arpent is a unit of area, but the side of a square arpent came to be used for linear description. The Spanish crown and the Mexican Government granted lands which were usually described in linear varas. Both the arpent and the vara have slightly different values in different States. The conversions most often needed are shown in the Standard Field Tables.
The measurements below are NOT from the manual.
Repeated division by 2 was the earliest choice for dividing lengths and portions into smaller units as one can very accurately divide by 2 multiple times, whereas division by 10, with accuracy, is much more difficult, especially as the ratio increases. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
