-/// the move's from and to squares, see chessprogramming.wikispaces.com/Butterfly+Boards
-typedef Stats<int16_t, 10368, COLOR_NB, int(SQUARE_NB) * int(SQUARE_NB)> ButterflyHistory;
+/// the move's from and to squares, see www.chessprogramming.org/Butterfly_Boards
+typedef Stats<int16_t, 14365, COLOR_NB, int(SQUARE_NB) * int(SQUARE_NB)> ButterflyHistory;
+
+/// At higher depths LowPlyHistory records successful quiet moves near the root
+/// and quiet moves which are/were in the PV (ttPv). LowPlyHistory is populated during
+/// iterative deepening and at each new search the data is shifted down by 2 plies
+constexpr int MAX_LPH = 4;
+typedef Stats<int16_t, 10692, MAX_LPH, int(SQUARE_NB) * int(SQUARE_NB)> LowPlyHistory;