For purposes of accurate measurement and calculation, Edward Gunter introduced, nearly three centuries ago, measurement by a chain of a hundred links and twenty-two yards or four rods in length. Its adoption decimalised the land-measures without disturbing them. Ten chains go to a furlong and ten square chains to an acre. Norden (‘Surveior’s Dialogue,’ 1610) mentions the ‘standard chaine, that is by the chaine of 16-1/2 foote.’ It was soon after this that the chain was increased to 66 feet or 4 rods, which length was a current unit, the ‘brede’ or acre-brede, the breadth of an acre. MEASURES OF LENGTH AND OF SURFACE In the following table each superficial unit is placed opposite the lineal unit of which it is the square: ─────────────────────────┬─────────────────────────────────────────────── LINEAL MEASURES │ SUPERFICIAL MEASURES ─────────────────────────┼─────────────────────────────────────────────── 12 inches 1 foot │ 144 square inches 1 sq. foot. 3 feet 1 yard │ 9 square feet 1 sq. yard. 5-1/2 yards 1 rod │ 30-1/4 square yards 1 sq. rod. │⎧ 40 square rods 1 rood 40 rods 1 furlong │⎨ (4 roods or 160 square rods 1 acre). │⎩ 40 roods (10 acres) 1 sq. furlong. 8 furlongs 1 mile │ 64 square furlongs (640 acres) 1 sq. mile. ─────────────────────────┴─────────────────────────────────────────────── SURVEYOR’S MEASURE ─────────────────────────────────┬───────────────────────────────────────────── 1 link (7·8 inches) ·22 yards.│1 square link ·048 sq. yds. 10 links 2·2 „ │100 square links 4·84 „ 100 links (1 chain) 22 „ │10,000 sq links (1 sq. chain) 484 „ 10 chains (1 furlong) 220 „ │10 sq. chains (1 acre) 4840 „ ─────────────────────────────────┴───────────────────────────────────────────── It must be remembered that _the length of the rod determined the length of the mile and the area of the acre_. This is shown in the table on the following page. BRITISH MILES AND ACRES DERIVED FROM DIFFERENT RODS IN LOCAL USAGE