Perch
Modern equivalent
16.5 feet = 5.0292 metres
A traditional land surveying unit (16.5 feet / 5.5 yards), synonymous with Pole and Rod.
The perch, rod or pole was the working unit of English land survey, and its value lies in what it squares to: forty square perches make a rood and 160 make an acre, so a surveyor pacing a field in perches could reach the acreage without leaving the ground. Three names for one length is unusual enough, but the word carries a further ambiguity. In the Channel Islands a perch is not a length at all but an area in its own right, a fortieth of a vergée, and it differs between the bailiwicks: roughly 44.7 square metres in Jersey and 39.4 in Guernsey, against the 25.29 that the English perch gives when squared. Both descend from Norman French practice, which is why they share a name, and anyone reading an island deed alongside an English one needs to know which is meant.