The Milton Keynes Boundary Walk is a circular walk approximately 65 miles long around the boundary of the Milton Keynes Unitary Authority; it is waymarked with the Oakleaf symbol.
In 2012 a group a local geocachers divided the walk into sections and set a series of over 300 caches along the boundary.
More information about the walk and caches can be found at the website Caching the Boundary.
The turquoise section of the walk is approximately 3.8 miles long. It starts at the north eastern edge of Oakhill Wood, heads west to the Stratford Road, and from there goes north west past Calverton, before heading north east and finishing near the outskirts of Stony Stratford.
There are 17 caches in this section, consisting of 15 traditional caches, 1 puzzle cache and 1 bonus cache (which contains a letter for the Gold Super Bonus cache).
Each (non-bonus) cache contains a letter, and some of these letters, in combination with the corresponding cache’s final coordinates, are needed in order to calculate the final coordinates of the bonus cache. The bonus cache is hidden near the middle of the turquoise section.
You are looking for a 1.3 litre camouflaged Clip Lock box.
The cache is not at the given coordinates.
If the final location of a turquoise cache containing bonus letter X is written as follows:
N 52° ??.XN1XN2XN3 W 000° ??.XW1XW2XW3
then the final location of the turquoise bonus cache can be calculated by using either of the following formulae:
N 52° 01.[JN2BW3PN2] W 000° 50.[GN3ON3MW3]
N 52° 01.[KW2AW3]*[IN1NN2] W 000° 50.[LN2HN3]*[DW2EW3]
Hence you need to find either the caches containing letters J, B, G, P, O and M, or the caches containing the letters K, A, I, N, L, H, D and E to determine the final location of the turquoise bonus cache.