Could be wrong, but throwin it out there. The cache log states to have a map of the park. Plot the first 4 caches on the map, draw a line from #1 to #3 and a line from #2 to #4, where these lines intersect is the spot for cache #5. Dead Reckoning is a term used when there is no clear line of site between 2 points, and you have to stand somewhere in the middle and triangulate between them. Def. going to follow this thread, please post your results.