This cache is not on the ancient Forest boundary of the 1240 Perambulation, but has been placed as a waymark between Wotesbrokelakesfote and Heighstone. More details about the Perambulation can be found on the cache page for the Dartmoor Forest Bonus. On the front page of the logbook is an adjustment to be made to the Bonus co-ordinates, which you will need to find the Bonus.
If doing this cache as a standalone, there is parking at Batworthy (waypoint below). If doing the Perambulation as a route, the next point on is Heighstone, now called Longstone. From Batworthy Corner, take the track that heads off slightly to your right up the hill. On the crest it meets another track heading towards Kestor Rock, but cross this and follow the track down to the stone.