Some information from the National Trust website:
Cissbury Ring is one of a series of hill-forts and with its ditch and ramparts is the second largest in England, the largest being Maiden Castle in Dorset. Overlooking 78 miles of coastline, this is an ideal site for defence. Archaeologists have found beach pebbles here, presumably hoarded as Iron Age sling shots. The hill was also an Armada beacon site. The breach in the rampart was made during World War II to make way for a 100lb gun, which fired at ships at sea. An anti-aircraft gun was sited in the hollow beside the breach.
Archaeological evidence shows that this strategic site was also important for flint production. Some of the strange hollows are the remains of Stone Age flint mines, dating back 5-6,000 years. Over 270 pits have been found. The flint was used to make tools, and there is evidence that it was exported as far away as the eastern Mediterranean. The shafts were over 23 metres deep, with many galleries radiating from the base.
On the lower slopes at the northern boundary, the often muddy hollow was once a dew pond and still provides a home for fairy shrimps. These tiny, extremely rare creatures can lie dormant for years until the pond fills with water. Vulnerable to predators, they cannot survive in permanent ponds.
This is a simple offset cache. The final location is in a high traffic area so stealth is required. The position is fairly exposed so please do your best to obscure the micro when you replace it.
Stage 1: Visit the trig and note the number on the flush bracket.
SABCD
Stage 2: The cache is hidden at:
N 50.51.(D+2)(A-1)(C+1) W 000 2(B+3).(B+1)(A)(D+2)