Editing Public Land Survey System (section)

===Measurement===

Distances were always measured in chains and links, based on [[Edmund Gunter]]'s [[Chain (unit)|66-foot measuring chain]].  The chain – an actual metal chain – was made up of 100 links, each being {{convert|7.92|in}} long. Eighty chains constitute one U.S. survey mile (which differs from the international mile by a few millimeters).  There were two chainmen, one at each end, who physically made the measurements, one of them typically also acting as "compassman" to establish the correct bearing at each chain placement.  In forested areas, it was essential for rapid progress and accuracy that the lead chainman follow the correct bearing at all times, since no straightening of the chain was possible without backtracking around trees and re-measuring.  It was also necessary to keep the chain level, since all surveying distances are based on the horizontal, not slope, distance.  In steep terrain, this meant shortening the chain, raising one end of the chain relative to the other, or both. In areas where measuring by chain was not possible, such as extremely steep terrain or water obstructions, distances were calculated by [[triangulation]].