http://gwydir.demon.co.uk/jo/units/area.htm

Rod, pole and perch are rather complicated. First, they are different names for the same unit of length, which is five and a half yards (see length page). To shorten the explanations, I use one unit rather than all three. Next, they could also be used as a unit of area. So a 10 perch allotment would be 5.5 yards wide by 55 yards long, or 10 square perch. To make my explanations clear, I say '(square) rod' to mean rod as a unit of area.

'tis as clear as mud now!