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Megalithic Mensuration 2. The Megalithic Yard and Rod.

3.2.1  Alexander Thom claimed to have arrived at close estimations of the lengths of the standards used in the construction of many prehistoric sites in Britain. These estimations is so finite that it could not have been resolved with confidence unless the original builders had adhered closely to very competent levels of surveying employing measuring devices of a standard comparable to modern surveyor's tape. By applying statistical methods to the numerous lengths derived from his data base of over 300 high class surveys Thom believed he could identify the ancient standard to plus or minus one hundredth of a foot;- 1 Megalithic Yard, (MY) = 2.720 British Feet = 0.829 metres. He also believed he could demonstrate the common use of a larger unit- the Megalithic Rod equalling 2.5 Megalithic Yards. 1 Megalithic Rod, (MR) = 2.5 MY = 6.8 feet = 2.073 metres.

A.Thom, 'Megalithic Sites in Britain' p.34/35 Today we use the yard as a standard unit of length. The word yard meant originally a rod of wood or a stick. The French verge has the same meaning and the Spanish word vara shows that this old length unit also meant originally a rod. In all three measures the idea was the same: the unit of length was carried about as a rod of wood just as today we carry a foot-rule or a metre stick. For our present discussion the most interesting is the vara, which has the following values in feet. Szymanski, 1956: 2.766 ft. Burgos, 2.7425 ft.Madrid. W. Latto and W. S. Olsen, private communication: 2.749 ft.Mexico. 2.778 ft.Texas and California. 2.75 ft.Peru. It is one of the objects of this chapter to demonstrate unequivocally the existence of a common unit of length throughout Megalithic Britain and to show that it's value was accurately 2.72 ft. We might speculate that this unit was left in the Iberian Peninsula by Megalithic people to become the vara of recent times and to be taken to America by Spain.

A.Thom, 'Megalithic Sites in Britain' p.34/35 Using all the data but excluding circles where the uncertainty in the measured diameter exceeds 1 ft, we desire to find definite answers to the following questions; 1. Can it be definitely established that a universal unit of length was in use in all parts of the country? 2. If so, what was its value? 3. Was it ever subdivided, and if so, how? 4. Was a different unit, perhaps a multiple, used for the longer distances? 5. In setting out circles was the measurement made to the inner side of the stone, to the centre of the stone, or to the outside? 6. Was the same unit used for circles, for alignments, and for the distances between circles?

3.2.2  Thom relied for his analysis on Broadbent's criterion,(1955), and Broadbent's Monte Carlo solution, (1956), His statistical approach is explained in pages 2 to 13 of 'Megalithic Sites in Britain'. He also offers more accessable presentations in histogram form illustrating the gathering of circle designs around certain sequences of diameters and perimeters, as in the series of diameters at 4, 8, 12, 16 MY....etc.                                           From A.Thom, Megalithic Sites in Britain p.46. Here it is readily seen how this long sequence of diameters, in multiples of 4 MY, produces an equally extensive series of perimeters in multiples of 5 Megalithic Rods. (MR). 1 MR = 2.5 MY. Another immediate appraisal of the existence of these standards, the MY and MR, may be made in Thom's alleged design for the Woodhenge post settings.                                                    A.Thom, Megalithic Sites in Britain p.74. For a closer appreciation of the Woodhenge design see Megalithic Maths p6. Integer design. Thom shows that many of the stone ring designs are intended to exhibit integers in their construction lengths. But for this persistence in using multiples of the two basic standards it may never have been possible to identify these lengths nor of unravelling the geometric thinking behind the designs of the more complex rings such as Woodhenge, Kerry Pole, Avebury. For more on integer design see Megalithic Maths 2.

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