The rood is a unit of area used in historic England with the symbol ro.
Its unit size is equal to 1/4 of an acre, 10,890 ft² or 1,012m². A rectangle equal to one furlong in length and one rod in width is one rood in area.
Its use was very important in surveying land because of the ease of conversion into acres from smaller sections of land.
The barn is a unit of area and is used in particle physics with the symbol b.
It represents approximately the area of the cross-section of a uraneum nucleus, so is very small compared to most other recognised units of area.
It is also used to measure the interaction of a nucleus with an electric field gradient in nuclear quadrupole and magnetic resonance.