- bool useClassical = abs(eg_value(pos.psq_score())) * 16 > NNUEThreshold1 * (16 + pos.rule50_count());
- bool classical = !Eval::useNNUE
- || useClassical
- || (abs(eg_value(pos.psq_score())) > PawnValueMg / 8 && !(pos.this_thread()->nodes & 0xF));
- Value v = classical ? Evaluation<NO_TRACE>(pos).value()
- : NNUE::evaluate(pos) * 5 / 4 + Tempo;
-
- if ( useClassical
- && Eval::useNNUE
- && abs(v) * 16 < NNUEThreshold2 * (16 + pos.rule50_count()))
- v = NNUE::evaluate(pos) * 5 / 4 + Tempo;
+ Value v;
+
+ if (!Eval::useNNUE)
+ v = Evaluation<NO_TRACE>(pos).value();
+ else
+ {
+ // scale and shift NNUE for compatibility with search and classical evaluation
+ auto adjusted_NNUE = [&](){ return NNUE::evaluate(pos) * 5 / 4 + Tempo; };
+
+ // if there is PSQ imbalance use classical eval, with small probability if it is small
+ Value psq = Value(abs(eg_value(pos.psq_score())));
+ int r50 = 16 + pos.rule50_count();
+ bool largePsq = psq * 16 > (NNUEThreshold1 + pos.non_pawn_material() / 64) * r50;
+ bool classical = largePsq || (psq > PawnValueMg / 4 && !(pos.this_thread()->nodes & 0xB));
+
+ v = classical ? Evaluation<NO_TRACE>(pos).value() : adjusted_NNUE();
+
+ // if the classical eval is small and imbalance large, use NNUE nevertheless.
+ if ( largePsq
+ && abs(v) * 16 < NNUEThreshold2 * r50)
+ v = adjusted_NNUE();
+ }