A survey Chain from Edmund Gunter's system having 100 metal links and being 66 feet, or 4 rods, in length. Used in land surveying. One chain (Gunter's Surveyor's)is 4 rods, 22 yards, or 66 feet. 1 ch (Gunter's Surveyor's) = 20.1168 m (SI base unit).
International survey foot defined as exactly 0.3048 meters by convention in 1959. This is the most common modern foot measure. US Survey may also be used but are nearly identical for short distances. 1 ft = 0.3048 m.