diff --git a/app/src/main/java/com/example/medilightv2android/managers/PiezoBVEstimator.kt b/app/src/main/java/com/example/medilightv2android/managers/PiezoBVEstimator.kt
index 7ad3fb5..635ea73 100644
--- a/app/src/main/java/com/example/medilightv2android/managers/PiezoBVEstimator.kt
+++ b/app/src/main/java/com/example/medilightv2android/managers/PiezoBVEstimator.kt
@@ -197,7 +197,10 @@ fun computeLrRatio(
     // Shrinkage toward prior
     val avgRatio = latResults.map { it.ratio }.average()
     val confidence = ((1.0 - avgRatio) / 0.10).coerceIn(0.0, 1.0)
-    return hw.lrPrior + (lrRaw - hw.lrPrior) * confidence
+    val result = hw.lrPrior + (lrRaw - hw.lrPrior) * confidence
+
+    // 하한 1.0: 원형보다 좁은 단면은 물리적으로 불가
+    return result.coerceAtLeast(1.0)
 }
 
 // ── Result ──