Venus and the Megalithic Yard

Those of you who are interested in the ancient measure, Proffesor Alexander Thom's megalithic yard (MY), would do well to investigate the book Civilization One by Christopher Knight and Alan Butler (ISBN 978-1-907486-09-8). Messers Knight and Butler investigate an early unit of measure which was accurate within millimeters from the northern Hebrides to southern Europe. The unit of measure has a relationship too with the Minoan culture's foot.
The first fact that comes as a surprise to many is that the old Summarian civilization used a circle of 366 degrees. That circle with its 366 divisions was obviously based on the length of the year (approximately 365 1/4 days). The diameter of the earth had early on been calculated by accurately measuring the length of one degree. The question has always been: How can you develop a measure using this fact?
You yourself can do a similar experiment: Working on the day of spring or autumn equinox, set up two poles of equal height, say 50 MY (Megalithic Yards) apart, in an E --> W direction, and two more poles in a N --> S direction. Measure the time it takes for the shadow of the first pole to be the same length as the shadow of the second pole. You must measure the shadows to better than a millimeter and the time to less than 1/10 second. The measurement results in a full polar circumference of the earth of 48,221,838 MY.
The ancient Sumerians used a base 6 for their calculations, so they separated each degree into 60 minutes and each minute into 6 seconds. When you divide this out, you find that one second of the full circumferance of the earth turns out to be 366 MY. You might call this a coincidence--but it isn't.
If you erect two poles separated by one degree of arc, then you can determine how long a star or a planet takes to traverse the distance between the two poles, measuring this time by the swing of a pendulum. The same mathematical trick that we use in casting our circles can be used to accomplish this. If you cast a circle of diameter 233 units and then divide it up using a 2-unit stick, you will find that you get one degree of arc per division. When you do this for a star, you find a pendulum length close to half a MY, but not quite, and certainly not within the accuracy to which the megalithic monuments were built.
It occurred to researcher Robert Lomas that perhaps the ancients used not a star but the planet Venus. Working with Christopher Knight (see above), Lomas had found that Venus was hugely important to the builders of megalithic sites. For example, New Grange was designed so that the light of Venus came into its central chamber for only a couple of minutes every eight years.
When you measure the transit of Venus between your two poles, you see that you get various results. This is because the apparent movement of Venus is regulated by the fact that it moves around the sun as the earth does. If you use a pendulum to measure its transit, when you measure the slowest transit, you get a pendulum length of exactly ½ MY--and we mean exactly: to better than 1 part in 3,000. Thus you have a method of developing the MY with very high accuracy no matter where on earth you are. True, in a very few places, such as high mountains or deep valleys, the swing of the pendulum will be slightly off. In most cases, though, this will result in an error of less than 1 part in 10,000.
Thus you can develop the MY with the most simple of tools: pieces of string, some form of plumb-bob weight, and a measuring stick (which can be of any length). It seems that our ancestors were far smarter than we thought: not just pointing and grunting ....
Why should you go to all this song-and-dance? Because the megalithic yard is the unit of measure we Wiccans use in casting our circles for spiritual work. Good enough?
By the way, Civilization One also explores liquid and cubic measure, and shows that they were probably developed for trade.