Perch
16.5 feet. (Johnstone, 1975, p.22)
The perch, as a unit of measure, can be traced back to pre-Saxon Britain. Circa 1300 A.D. the foot was standardized in Britain. With the pre-existing measurement of the “perch” already defining much of the land, the length (in the new standard foot) was established to be 16.5 feet.
http://www.pobonline.com/articles/86512-web-exclusive-the-surveyors-rod
