It's all done by eye - and with rods and string. Bits of notched wood.

There's a kite pattern in the sky - at this moment. The moon on one side of the earth, opposite to venus, which has saturn and uranus equally disposed thirty degrees away.

There are three curricks close together at Kirkhaugh - http://www.themodernantiquarian.com/post/20531 - it seems just about possible that the stars we know as Orion's Belt may have set behind these markers at a certain time of the year, viewed from the main site a good mile away. The only test is to try it. Compensation for procession may be achieved by stepping on a box.