The South Wonston Long Barrow is a cemetery consisting of three long barrows dating back to 3000 - 2,400 BC and two Bronze Age round barrows from 2,000 - 1,000 BC. The people who built the barrows were among the earliest farmers in Southern Britain. These early farmers chose to bury their dead on a crest of chalk downland midway between the River Dever to the north and the River Itchen to the south.
The co-ordinates are from the information board at the Long Barrow: The air veiw photo looking south was taken in AB3C; the number of skulls on the board = D; the number of people in the picture = E; the original height of the Long Barrow = Fm; the number of words in the board title = G.
The final cache co-ordintes = N51oC (G+D). (F+A) D G , W001oA B. C (G-F) (B-E)
You are looking for a small clip-lock plastic container big enough for a log book and small swappables.