IIRC (read the book ages ago when much younger) , the theory was that by using the 56 Aubrey holes to count, say, by moving a pole from one hole to another once a year, an eclipse could be predicted to occur every 18th or 19th year. I always wondered why this was never simulated, and I guess the answer is that it would not work.

https://en.wikipedia.org/wiki/Aubrey_holes#Archaeoastronomy_...