diff --git a/app/src/main/java/com/example/medilightv2android/ui/views/monitoring/PlacementGuideView.kt b/app/src/main/java/com/example/medilightv2android/ui/views/monitoring/PlacementGuideView.kt
index 3eb604f..139abad 100644
--- a/app/src/main/java/com/example/medilightv2android/ui/views/monitoring/PlacementGuideView.kt
+++ b/app/src/main/java/com/example/medilightv2android/ui/views/monitoring/PlacementGuideView.kt
@@ -1812,6 +1812,7 @@ private fun computePlacementGuide(
     val centerCh = hw.centerCh
 
     val depths = mutableListOf<Double>()
+    val missingCenters = mutableListOf<Int>()
     for (localIdx in centerCh.indices) {
         val ch = centerCh[localIdx]
         val w = if (ch < walls.size) walls[ch] else null
@@ -1819,12 +1820,28 @@ private fun computePlacementGuide(
             val rawDepth = (offset + w.second * dps) - (offset + w.first * dps)
             val theta = degAll[ch] * Math.PI / 180.0
             val corrected = rawDepth * kotlin.math.cos(theta)
-            if (corrected > 0) depths.add(corrected)
+            if (corrected > 0) depths.add(corrected) else missingCenters.add(ch)
+        } else {
+            missingCenters.add(ch)
         }
     }
 
-    if (depths.size < 2) {
-        return PlacementGuideResult("Start over from above the pubic bone", "arrow.up", 10,
+    // 측정 단계 BV 게이트와 정렬 (effectiveCenterWalls >= 4) — 4개 center 모두
+    // 잡혀야만 GREEN 통과. 정렬 OK 직후 측정 시 ch3 missing 으로 BV SKIP 되던 케이스 차단.
+    if (depths.size < 4) {
+        val pubicMissing = 3 in missingCenters    // ch3 = 치골 쪽 (bottom of sensor)
+        val navelMissing = 0 in missingCenters    // ch0 = 배꼽 쪽 (top of sensor)
+        val (hint, icon) = when {
+            missingCenters.size >= 2 ->
+                Pair("Adjust position — multiple channels missing", "arrow.up")
+            pubicMissing ->
+                Pair("Slide up slightly ↑  (ch3 missing)", "arrow.up")
+            navelMissing ->
+                Pair("Slide down slightly ↓  (ch0 missing)", "arrow.down")
+            else ->
+                Pair("Adjust position slightly — center channel missing", "arrow.up")
+        }
+        return PlacementGuideResult(hint, icon, 30,
             phase = PlacementPhase.GREEN, nextPhase = PlacementPhase.VERTICAL)
     }