What's a Pole?
Every system, past and present, was developed to be both logical and to meet the measurement needs of its time...
Old land measures in England
Based on Roman and Anglo-Saxon measurements, the foot, yard (three feet) and pole (also called a rod, and equal to 5.5 yards) were used to measure land. Older measures included the furlong, originally the distance a pair of oxen could plough a furrow without resting, i.e. a furrow long, and the acre, originally the area that could be ploughed by a pair of oxen in a day. The furlong became defined as 40 poles, and the acre as a rectangle measuring one furlong (or 40 poles) by four poles. The rood was an area measuring one furlong (or 40 poles) x one pole, and was 1/4 acre. A perch was a square pole. Eight furlongs make a mile, which means that a square mile contains 640 acres.
Gunter's Link
In 1620, Edmund Gunter (1581-1626), Professor of Astronomy at Gresham College, London and a mathematician, published his rationale and design for a new system of land measurement. This new system cleverly combined the traditional English land measures with a new decimal system. Calculations were easier, and his system was rapidly accepted in the UK and US. It was based on a chain consisting of 100 iron links. Each link measured 7.92 inches, and a chain measured 66 feet (22 yards). Because there were 100 links in a chain, sub-divisions of chains could be expressed in decimals, so that 7.08 chains would be 7 chains and 8 links.
1 link = 66/100 foot (or 7.92 inches)
25 links = 1 pole (also known as a rod)
100 links = 4 poles = 1 chain
1000 links = 10 chains = 1 furlong
8000 links = 8 furlongs = 1 mile
The relationships of some of the above measures to inches, feet and yards are as follows:
66/100 foot = 1 link = 7.92 inches
1 pole = 5.5 yards = 16.5 feet
1 chain = 22 yards = 66 feet
1 furlong = 10 chains = 220 yards = 660 feet
A chain is, incidentally, also the distance between the stumps of a cricket pitch.
Area measurement
The pole is a linear measure, but the word 'pole' is also used for a square pole ie a square measuring one pole on its sides (ie a perch).
1 square pole = 1 perch = 5.5 yards x 5.5 yards
160 square poles = 1 acre
1 furlong x 1 chain = 1 acre
1 acre = 4840 square yards
Relating these to allotments...
An allotment plot of 5 poles is 5 square poles in area.
1 square pole = 5.5 x 5.5 = 30.25 square yards or 25.3 square metres.
5 square poles = 151.3 square yards or 126.5 square metres.
32 plots of 5 square poles = 1 acre.
And if you've got this far, you might be interested in another old measure, the fathom, used to measure the depth of water. The word means the spread of a person's outstretched arms (Old English word fæðm, from the Danish via the Vikings word "favn", maybe also the Old High German word "fadum", in Middle English fathme - Wikipedia). Originally varying from 5 to 7 feet, it became defined as either 6.0 feet or (British Admiralty) 1/1000 of a nautical mile = 6.08 feet. The difference was too small to matter in practice. A cable length (from the era of sail) was originally the length of a ship's cable, later defined as 1/10 nautical mile, or 100 British Admiralty fathoms. Modern charts show depths in metres.