This series comprises four traditional caches, each of which
contains a ten digit number. Any three of these numbers provide
enough information to find the bonus cache - which three will you
choose? The numbers are labelled A, B, C and
D, and sum to 10,000,000,000: the tenth root of a googol.
The grid reference of the final cache (in grid square SP) can be
calculated as A – B + C – D.
A quincunx is an arrangement of five dots as seen on the
fifth side of a playing die, with one at each corner of a square,
and one in the centre. It is named after the Roman coin worth five
twelfths (quinque + uncia) of an as,
emblazoned with that pattern.
This cache is near the site of the old Wolvercote Halt railway
station, which served the London and North Western Railway and
later the London, Midland and Scottish Railway, from 1905 to 1926,
as part of the "Varsity Line" between Oxford and Cambridge.
The container is a magnetised Tic-Tac box, and should be at
least a foot above ground level. Please replace it upside-down so
that water doesn't get in if there are heavy rains. The number for
the bonus cache is on the side. You will need to bring your own
writing implement.