diff --git a/game/reconstructed/mech4.cpp b/game/reconstructed/mech4.cpp
index a56b001..d0c87ca 100644
--- a/game/reconstructed/mech4.cpp
+++ b/game/reconstructed/mech4.cpp
@@ -2095,6 +2095,32 @@ void
 					legCycleSpeed = 0.0f;
 				(void)AdvanceLegAnimation(dt);		// joints only; travel = DeadReckon
 
+				// TURN-STEP rate probe (BT_TRNRATE, 0.5s): body rotation rate vs trn clip advance.
+				if (getenv("BT_TRNRATE"))
+				{
+					static bool  s_tinit = false;
+					static float s_tYaw = 0.0f, s_tFrm = 0.0f, s_tAcc = 0.0f, s_tRot = 0.0f, s_tAdv = 0.0f;
+					YawPitchRoll _typ; _typ = localOrigin.angularPosition;
+					const float yaw = (float)_typ.yaw, frm = (float)legAnimation.currentFrame;
+					if (s_tinit)
+					{
+						float dy = yaw - s_tYaw; if (dy > 3.14159f) dy -= 6.28319f; if (dy < -3.14159f) dy += 6.28319f;
+						s_tRot += (dy < 0.0f) ? -dy : dy;
+						const float df = frm - s_tFrm;
+						if (df > 0.0f) s_tAdv += df;
+					}
+					s_tYaw = yaw; s_tFrm = frm; s_tinit = true;
+					s_tAcc += dt;
+					if (s_tAcc >= 0.5f)
+					{
+						DEBUG_STREAM << "[trnrate] bodyRot/s=" << (s_tRot / s_tAcc) << "rad"
+							<< " legFrm/s=" << (s_tAdv / s_tAcc)
+							<< " legState=" << (int)legStateAlarm.GetLevel()
+							<< " turnDemand=" << MappingMapper()->turnDemand << "\n" << std::flush;
+						s_tAcc = 0.0f; s_tRot = 0.0f; s_tAdv = 0.0f;
+					}
+				}
+
 				// Cadence-vs-travel sync probe (0.25s, ~4 flush/s -- cheap).  Compares
 				// the leg CADENCE input (bodyTargetSpeed / legCycleSpeed) against the
 				// ACTUAL dead-reckoned ground speed; if the legs are in sync the two