What is syzygy probe depth?

Syzygy tablebase options: Komodo has a number of UCI options to control its use of the tablebases. If SyzygyProbeDepth = 10, it will probe TBs in nodes of the search tree that would otherwise be searched to depth 10 or higher. For example Stockfish 5 (development versions) has a syzygy probe depth scale of 1-100. Hi I wonder if anyone here could tell me what is the ideal syzygy probe depth for Stockfish and Houdini 4 ? I have all the Syzygy EGTB on a 360. The Syzygy 6-men EGTB system is the recommended table base solution for. It can be Syzygy, Nalimov or Gaviota.