This post continues the ancient Welsh view of measuring the land:
"And then they made the measure of the legal acre from the barleycorn. Three lengths of the barleycorn in the inch; three inches in the palmbreadth; three palmbreadths in the foot. Four feet in the short yoke, sixteen in the long yoke; a rod as long as the long yoke in the caller's hand, and as far as he reaches with it, his arm stretched out, is the two limits, that is, the width of the legal acre; and thirty times the rod is its length."
Again from the barleycorn:
three lengths of the barleycorn = 1 inch
three inches in the palmbreadth
three palmbreadths = 1 foot [would be about 9 inches in today's measurements]
four feet [12 palmbreadth] in the short yoke [a yoke is used to plow the land ca. 36 inches]
sixteen feet in the long yoke [a yoke used for two animals ca. 12 feet long]
1 rod = the long yoke + "caller's hand" = roughly 14 - 15 feet
legal acre = 2 rods (width) x 30 rods (length) = roughly 30 ft. x 450 ft.
Thus, a "long yoke" (two animals) could plow up and down the legal acre in two passes. A "short yoke" (single animal) would take four passes of the plow.
Taken from: Hywel Dda The Law, Law Texts from Medieval Wales, translated and edited by Dafydd Jenkins, Gomer Press, 1990, p.120.