In reply to TryfAndy:
that should do it.
Where on dartmoor are you planning? Beware the firing ranges can get really boggy, not dangerously so, just unpleasant.
I went on a brilliant walk a couple years ago that went by blackator copse, meldon reservoir, past Okehampton castle, through the camp then up to yes tor and high willhays.
We also did a walk to yes tor from two bridges, but this came up through the ranges, and had to deal with very wet, really lumpy terrain and so was not nearly as pleasant