The value is 42500 / 19008 and this is a Thom system numerator and an Imperial system denominator.
19008 / 5280 = 3.6.
Thom's system works with root 3 as 1.7333r and the imperial works with 99/70 as used by Crowhurst at Carnac.
In ths book the suggested method for the calculation of Pi is iterative using succesive stages to eventually hit the very closest approximation to real Pi. The same approach is suggested for square roots.
{iterative - repetition of a mathematical or computational procedure applied to the result of a previous application, typically as a means of obtaining successively closer approximations to the solution of a problem.)
On page 47 of his first book Thom gives the following table of diameters in megalithic yards.
The Aubrey circle 105
Avebury inner rings 125
Brodgar circle in the Orkneys 125
Stanton Drew circle 137 or 137.5
Since the Megalithic yard as a radius translates to 2.666r Megalithic feet in a circumference interpreting Thom's data is as follows
Stonehenge circle 280 megalithic feet
Avebury inner circle 333.333r megalithic feet
Brodgar circle 333.333r megalithic feet
Stanton Drew 365.333r megalithic feet
Stanton Drew 366.666r megalithic feet (2nd interpretation)
Since Stonehege represents 2912 solar days (see the book 'The Eclipse) the following pro rata totals can be calculated based on an eight year cycle of solar days
Stonehenge 2912 divide by 3.4666r to get 840
Avebury 3466.666r divide by 3.4666r to get 1000
Brodgar 3466.666r divide by 3.4666r to get 1000
Stanton Drew 3499.466r divide by 3.4666r to get 1096
Stanton Drew 3813.333r divide by 3.4666r to get 1100
3.4666r was used as a unit of interpretation
Surely the dark glass is beginning to clear.