diff --git a/USER_GUIDE.md b/USER_GUIDE.md
index dab369e..08a8597 100644
--- a/USER_GUIDE.md
+++ b/USER_GUIDE.md
@@ -1,6 +1,7 @@
 # VesiScan-Basic User Guide
 
 ## App Version: VBTAND0101
+## Last Updated: 2026-05-11
 
 ---
 
@@ -23,17 +24,17 @@
 ## 2. Connecting the Device
 
 1. Tap **Start** on the Home screen
-2. The app will scan for nearby VesiScan devices
+2. The app will scan for nearby VesiScan devices (sorted alphabetically)
 3. When your device appears in the list, tap it to connect
 4. **Complete the Bluetooth pairing** when the system dialog appears
-   - Do NOT press Cancel — the app will not proceed without pairing
+   - A "Pairing Required" dialog will guide you through the process
+   - Tap **Pair** on the system Bluetooth dialog — canceling will block the connection
+   - The app waits up to 30 seconds for pairing to complete
 5. Once paired, you will move to the Personalization screen
 
 ### Personalization
-- Set your **posture** (standing/sitting/lying)
-- Set the **sensor position**
-- Set the **Max Volume** (default: 500 mL)
-- Tap **Next** to proceed to Sensor Alignment
+- Set your **Max Volume** (200-800 mL, default: 500 mL)
+- Tap **Continue** to proceed to Sensor Alignment
 
 ---
 
@@ -41,45 +42,49 @@
 
 This step ensures the sensor is positioned correctly over your bladder for accurate measurement.
 
-### Step 1: Vertical Alignment
+### Before Starting
+- Place VesiScan above the pubic bone
+- Apply ultrasound gel between the sensor and your skin
+- Tap the **Start Alignment** button (large orange button)
 
-1. **Place the VesiScan-Basic device just above your pubic bone**
-2. Apply ultrasound gel between the sensor and your skin
-3. Tap the **Start Alignment** button
-4. The app will begin scanning and provide direction:
-   - **"Raise the sensor up"** — slide the device upward toward your navel
-   - **"Lower the sensor down"** — slide the device downward toward your pubic bone
-   - **"Raise the sensor slightly"** / **"Lower the sensor slightly"** — make small adjustments
-5. Move the sensor **slowly, 1-2mm at a time**
-6. When the vertical position is correct, the app will show **Step 2/3**
+### Step 1/3: Vertical Alignment
 
-> The hint text will show animated dots (e.g., "Raise the sensor up.", "Raise the sensor up..", "Raise the sensor up...") to indicate the system is actively scanning.
+The app will begin scanning and provide direction:
+- **"Slide up ↑"** — slide the device upward toward your navel
+- **"Slide down ↓"** — slide the device downward toward your pubic bone
+- **"Slide up slightly ↑"** / **"Slide down slightly ↓"** — make small adjustments
+- Move the sensor **slowly, 1-2mm at a time**
+- When the vertical position is correct, the app will show **Step 2/3**
 
-### Step 2: Lateral Alignment
+> The hint text will show animated dots (e.g., "Slide up ↑.", "Slide up ↑..", "Slide up ↑...") to indicate the system is actively scanning.
 
-1. The app will first show **"Checking left/right balance..."** for a few seconds
+### Step 2/3: Lateral Alignment
+
+1. The app will first show **"Checking..."** for a few seconds
 2. Then it will guide you:
-   - **"Move left"** — slide the device to the left
-   - **"Move right"** — slide the device to the right
+   - **"Slide left ←"** — slide the device to the left
+   - **"Slide right →"** — slide the device to the right
 3. Adjust until both lateral sensors (CH4 and CH5) detect the bladder equally
 4. When balanced, the app will show **Step 3/3**
 
-### Step 3: Final Check (Green Zone)
+### Step 3/3: Final Check (Green Zone)
 
-1. The app checks overall alignment quality
-2. If everything is optimal, the hint will show **"Optimal position!"**
-3. The screen will hold this state for **7 seconds** to confirm stability
-4. Tap **Alignment Complete** to proceed to the measurement screen
+1. The app checks overall alignment quality (CV + LR deviation)
+2. If everything is optimal, the hint will show **"In position!"**
+3. The screen background turns green and holds this state for **7 seconds** to confirm stability
+4. The **Start Scanning** button (green) becomes active
+5. Tap **Start Scanning** to proceed to the measurement screen
 
 ### If Alignment is Lost
-- If the sensor shifts significantly after reaching Optimal:
-  - The app will show **"Position lost. Place sensor above pubic bone, then press Start"**
+- If the sensor shifts significantly after reaching "In position!":
+  - The app allows up to **3 consecutive failures** before exiting GREEN
+  - After 3 failures: **"Position lost. Restart above pubic bone."**
   - The scanning will stop automatically
   - Re-place the sensor and tap **Start Alignment** again
 
 ### If the Sensor is Detached
 - If the sensor loses contact with skin:
-  - The app will show **"Sensor detached. Place above pubic bone, then press Start"**
+  - The app will show **"Sensor detached. Restart above pubic bone."**
   - Re-attach the sensor with gel and tap **Start Alignment**
 
 ### Tips
@@ -111,7 +116,7 @@ After alignment, you will see the main measurement screen with a donut chart.
    Current Measurement    |     65%
         280 mL            |   325/500 mL
         
-   [Void/Catheterize] [Auto] [Spot]
+   [Void/Catheterization] [Auto Scan] [Single Scan]
 ```
 
 ### Understanding the Display
@@ -127,48 +132,47 @@ After alignment, you will see the main measurement screen with a donut chart.
 
 ---
 
-## 5. Auto Measurement
+## 5. Auto Scan
 
-1. Tap the **Auto** button (orange)
-2. The device will measure continuously every ~1.5 seconds
+1. Tap the **Auto Scan** button (orange)
+2. The device will measure continuously (minimum 800ms interval)
 3. For the first 5 measurements, the display will show **"—"** (collecting data)
-4. After 5+ measurements, the **trimmed mean** value will be displayed
+4. After 5+ measurements, the **trimmed mean** value will be displayed (10-sample window, top/bottom excluded)
 5. The donut chart will update every 5 seconds
-6. Tap **Stop** (red) to end Auto measurement
+6. Tap **Stop Scan** (red) to end Auto measurement
 
 ### Auto Measurement Failure
-- If measurements fail **5 times in a row** (sensor shifted or lost contact):
-  - A dialog will appear: **"Sensor Position Issue"**
-  - Tap **Go to Alignment** to re-align the sensor
+- If 2+ channels fail **5 times in a row** (sensor shifted or lost contact):
+  - A dialog will appear: **"Position lost. Restart from alignment"**
+  - Tap **Realign** to re-align the sensor
   - Or tap **Dismiss** to stay on the measurement screen
 
 ---
 
-## 6. Spot Measurement
+## 6. Single Scan (Spot)
 
-1. Tap the **Spot** button
-2. The device will take **5 consecutive measurements** (~4 seconds total)
+1. Tap the **Single Scan** button
+2. The device will take **5 consecutive measurements** (~4 seconds total, max 8 attempts)
 3. A **spinner** will show during measurement
 4. The result (trimmed mean of 5 readings) will be displayed immediately
 5. The donut chart and Current Measurement card will update
 
-> During Spot measurement, the Auto and Void buttons are disabled.
+> During Single Scan, the Auto Scan and Void buttons are disabled.
 
 ---
 
-## 7. Void / Catheterize
+## 7. Void / Catheterization
 
-1. Tap the **Void / Catheterize** button
+1. Tap the **Void / Catheterization** button
 2. The current measurement is recorded to the voiding diary
 3. The catheter count decreases by 1
 4. The bladder level resets to 0
-5. A toast message **"Voiding recorded"** will appear
+5. A toast message **"Recorded"** will appear
 
 ### Managing Catheters
 - The catheter count is shown at the top of the screen (hospital icon + number)
 - **Tap the catheter count** to add more catheters
 - Enter the number and tap **Add**
-- Default starting count: **15 catheters**
 
 ---
 
@@ -192,11 +196,6 @@ Tap the **gear icon** at the top right to open settings.
 | SG Filter | Savitzky-Golay noise filter on/off |
 | Post Max | Maximum sample index for wall detection (filters floor reflections) |
 
-### Saving Settings
-- Adjust values using sliders and toggles
-- Tap **Save** to apply and close
-- Tap **Cancel** to close without changes (note: slider changes apply in real-time)
-
 ---
 
 ## 9. Navigation
@@ -214,14 +213,13 @@ Tap the **gear icon** at the top right to open settings.
 
 | Problem | Solution |
 |---------|----------|
-| "Place sensor above pubic bone" won't go away | Make sure the sensor is attached with gel, then press **Start Alignment** |
-| Alignment keeps showing "Raise/Lower" | Move the sensor **very slowly**, 1-2mm at a time |
+| "Place VesiScan above the pubic bone" won't go away | Make sure the sensor is attached with gel, then press **Start Alignment** |
+| Alignment keeps showing "Slide up/down" | Move the sensor **very slowly**, 1-2mm at a time |
 | Auto measurement shows "—" | Wait for at least 5 measurements to accumulate |
 | Donut chart value doesn't change | Max volume updates every 5 seconds |
-| Spot measurement takes too long | Each Spot takes ~4 seconds (5 readings) |
-| "Sensor Position Issue" dialog appears | The sensor may have shifted — go to Alignment |
+| Single Scan takes too long | Each scan takes ~4 seconds (5 readings) |
+| "Position lost" dialog appears | The sensor may have shifted — go to Alignment |
 | Bluetooth connection lost | The app will attempt auto-reconnect (up to 5 times) |
-| App freezes on measurement screen | Check BLE connection, try disconnecting and reconnecting |
 | Pairing dialog appears but app won't proceed | You must tap **Pair** — canceling will block the connection |
 
 ---
@@ -230,13 +228,10 @@ Tap the **gear icon** at the top right to open settings.
 
 | LED State | Meaning |
 |-----------|---------|
-| Green blink (0.5s) | Bluetooth scanning |
-| Green on 1s / off 3s | Device idle (not attached) |
-| Orange blink (1s) | Sensor Alignment in progress |
-| Green solid | Alignment complete (Optimal position) |
-| Orange fast blink (3Hz) | Error detected |
-| Orange solid | Charging |
-| Blue solid | Charging complete |
+| State 0 | OFF (default) |
+| State 4 | Sensor detached warning |
+| State 5 | Alignment searching (orange) |
+| State 6 | Alignment complete / In position (green) |
 
 ---
 
diff --git a/VesiScan_Android_Pipeline_Summary.md b/VesiScan_Android_Pipeline_Summary.md
index 761d868..c953b2c 100644
--- a/VesiScan_Android_Pipeline_Summary.md
+++ b/VesiScan_Android_Pipeline_Summary.md
@@ -2,7 +2,7 @@
 
 ## 작성일: 2026-04-23
 ## 작성자: dwjang
-## 마지막 업데이트: 2026-05-09 (v4) — VBTAND0101
+## 마지막 업데이트: 2026-05-11 (v5) — VBTAND0101
 
 ---
 
@@ -383,34 +383,46 @@ Android: estimateBladderVolume6ch(6채널)
          [CH0]  0°      ← 가장 위 (배꼽쪽, y=21mm)
 ```
 
-## 방향 안내 로직 — 3모드 (2026-05-07 업데이트)
+## 방향 안내 로직 — 3모드 (2026-05-11 업데이트)
 
 개발자 모드 Settings에서 전환 가능: **Gradient** (기본) / Boundary / **SWEEP**
 
+### 조작 흐름 (Start 버튼 필수)
+
+```
+화면 진입 → "Place VesiScan above the pubic bone, then press Start"
+    ↓ Start Alignment 버튼 탭 (96dp 대형)
+전체 상태 리셋 → 1초 간격 연속 스캔 시작
+    ↓
+VERTICAL → LATERAL → GREEN (순차, 건너뛰기 없음)
+    ↓ GREEN 7초 유지 + 3회 연속 실패 안 하면
+Start Scanning 버튼 활성화 (초록색)
+```
+
 ### Gradient 모드 (기본) — 신호 길이 비교
 
 ```
-시작: 치골 위 → 위로 올림
+시작: 치골 위
 
 1단계 VERTICAL:
   0~1채널: ch0/ch1 감지→↑, ch2/ch3 감지→↓
   2+채널: weighted center gradient
     weightedCenter = Σ(ch_pos × len) / Σ(len)
     gradient = weightedCenter - 1.5
-    gradient > 0 → ↓ (ch3쪽 길다 = 방광 아래)
-    gradient < 0 → ↑ (ch0쪽 길다 = 방광 위)
-    |gradient| < 0.4 + lenVariation < 0.5 → 상하 OK
+    gradient > 0 → "Slide down ↓" (ch3쪽 길다 = 방광 아래)
+    gradient < 0 → "Slide up ↑" (ch0쪽 길다 = 방광 위)
+    |gradient| < 0.3 + centerDetected >= 4 → "Checking..." → LATERAL
 
 2단계 LATERAL:
-  |len4 - len5| ≤ 10 sample → 바로 GREEN
-  lrSymmetry ≥ 0.5 → GREEN
-  아니면 len 차이 방향으로 안내
+  |len4 - len5| ≤ 10 sample → "Final check..." → GREEN
+  lrSymmetry ≥ 0.5 → "Final check..." → GREEN
+  아니면 "Slide left ←" / "Slide right →"
 
 3단계 GREEN:
-  CV ≤ 0.12 (10회마다 +0.03 완화)
-  |lrDev| ≤ 0.35
-  둘 다 통과 → Green!
-  CV만 간당간당 → "Almost there..." (GREEN에 머물며 재시도)
+  CV ≤ threshold (V0=0.07, V1/V2=0.10, 5회마다 +0.03 완화)
+  |lrDev| ≤ 0.20
+  둘 다 통과 → "In position!" (7초 hold)
+  3회 연속 실패 → "Position lost. Restart above pubic bone." + 스캔 중지
 ```
 
 ### SWEEP 모드 (CKLaw) — 위에서 아래로 쓸어내리기
@@ -446,26 +458,44 @@ Android: estimateBladderVolume6ch(6채널)
 
 | 상수 | 값 | 의미 |
 |------|-----|------|
-| DEFAULT_CV_THR | 0.12 | 기본 CV 임계 (10회마다 +0.03 완화) |
-| DEFAULT_LR_DEV_THR | 0.35 | LR 비대칭 임계 |
+| DEFAULT_CV_THR | V0=0.07, V1/V2=0.10, 기타=0.08 | 기본 CV 임계 |
+| CV 완화 | +0.03 per 5 scans | 5회마다 임계값 증가 |
+| DEFAULT_LR_DEV_THR | 0.20 | LR 비대칭 임계 |
 | 절대 LR 차이 | ≤10 sample | LATERAL 즉시 통과 |
 | R-peak tolerance | 1.5mm | SWEEP 모드 GREEN gate |
-| 디바운스 | 1.5초 | phase 전환은 즉시, 같은 phase 힌트만 디바운스 |
+| GREEN hold | 7초 | GREEN 진입 후 최소 유지 시간 |
+| GREEN exit | 3회 연속 실패 | hold 이후 이탈 조건 |
+| 디바운스 | 1.5초 (같은 phase) / 3초 (phase 전환) | |
+| Phase 보호 | 3스캔 | phase 전환 후 힌트 강제 유지 |
+
+### 힌트 텍스트 (모든 방향 힌트에 화살표 포함)
+
+| 상황 | 텍스트 |
+|------|--------|
+| 상하 이동 | "Slide up ↑" / "Slide down ↓" / "Slide up slightly ↑" / "Slide down slightly ↓" |
+| 좌우 이동 | "Slide left ←" / "Slide right →" |
+| 확인 중 | "Checking..." |
+| 최종 확인 | "Final check..." |
+| 최적 위치 | "In position!" |
+| 위치 이탈 | "Position lost. Restart above pubic bone." |
+| 센서 미부착 | "Sensor detached. Restart above pubic bone." |
 
 ## 연속 스캔 동작
 
 ```
-"Start Scanning" 버튼 탭
+"Start Alignment" 버튼 탭 (waitingForStart → false)
+    ↓
+전체 상태 리셋 (phase, score, debounce, greenFail 등)
     ↓
 즉시 첫 스캔 (maa 6채널)
-    ↓ 결과: CV, 방향, Score 표시
-3초 대기
+    ↓ 결과: CV, 방향, Score 표시 (28sp 대형 힌트)
+1초 대기
     ↓
-자동 재스캔 (repeatCount 증가 → threshold 완화)
+자동 재스캔 (scanCount 증가 → CV threshold 완화)
     ↓
-... 반복 (사용자가 Stop 누를 때까지)
+... 반복 (GREEN 도달 or 이탈 시 자동 중지)
 
-is_pass = true → Lock → "Start Measurement" 활성화
+is_pass = true → Lock → 7초 hold → "Start Scanning" 버튼 활성화
 ```
 
 ---
@@ -504,20 +534,22 @@ Spot 버튼 탭
 화면에 "305 ml" 표시! (도넛차트 + 레벨 업데이트)
 ```
 
-## Auto 모드 (2026-05-07 업데이트)
+## Auto Scan 모드 (2026-05-11 업데이트)
 
-별도 Auto 버튼으로 자동 반복 측정:
-- 1.5초 간격 자동 측정
-- 첫 5회: "Measuring... (n/5)" 로딩 표시
-- 5회 이상: **sliding window trimmed mean** (10개 윈도우) → 안정된 값 표시
-- Stop 버튼으로 종료
+"Auto Scan" 버튼으로 자동 반복 측정:
+- 최소 800ms 간격 자동 측정 (BLE maa throttle 보장)
+- 첫 5회: "—" 표시 (데이터 수집 중)
+- 5회 이상: **sliding window trimmed mean** (10개 윈도우, 최대/최소 각 1개 제외 → 8개 평균)
+- "Stop Scan" 버튼으로 종료
+- Auto fail: 2ch+ missing 5회 연속 → "Position lost. Restart from alignment" 다이얼로그
 
-## Spot 모드 (2026-05-07 업데이트)
+## Single Scan 모드 (2026-05-11 업데이트)
 
-Spot 버튼 1탭 → **3회 측정 → median** (중간값 깜빡임 없음):
-- 최대 6회까지 재시도 (유효값 3개 수집 목표)
-- 측정 간격 300ms (BLE 겹침 방지)
+"Single Scan" 버튼 1탭 → **5회 측정 → trimmed mean**:
+- 최대 8회까지 재시도 (유효값 5개 수집 목표, 최소 3개)
+- 측정 간격: maa 800ms throttle이 간격 보장
 - 중간 값 화면 미표시 (isSpotInProgress 플래그)
+- 1초 쿨다운 후 재사용 가능
 
 ## 측정 실패 시 자동 재시도
 
@@ -1058,7 +1090,15 @@ Start Scanning (3초 간격 자동 반복)
 ║ PASS → LED 6 (ALIGN_COMPLETE) + Lock  ║
 ╚═══════════════════════════════════════╝
     ↓ Green!
-"Start Measurement" 버튼 활성화
+"Start Scanning" 버튼 활성화 (초록, 96dp)
+```
+
+### 태블릿 대응
+
+```
+fontScale = (screenWidth / 360f).coerceIn(1.0, 1.8)
+→ 폰(360dp)=1.0배, 태블릿(600dp+)=~1.6배
+버튼/힌트 텍스트, InfoCard, 배터리/카테터 표시 등 전체 적용
 ```
 
 ### 패킷 드랍 대응
@@ -1267,6 +1307,13 @@ ADC 파싱 시 Big/Little Endian을 자동 감지:
 | ADC CSV 저장 | ✅ 완료 | 세션별 파일 |
 | Canvas 하복부 실루엣 | ✅ 완료 | PNG 제거, CKLaw Bezier torso |
 | i18n (한국어/영어) | ✅ 완료 | strings.xml |
+| UI 텍스트 통일 | ✅ 완료 | revised 문서 반영 (Slide up ↑, In position! 등) |
+| 태블릿 대응 | ✅ 완료 | fontScale, 비율 기반 레이아웃, 힌트/버튼 확대 |
+| 페어링 다이얼로그 | ✅ 완료 | bonding 대기 중 안내 표시 |
+| 앱 아이콘 | ✅ 완료 | 방광이 캐릭터 PNG (5 density) |
+| Placement 화살표 수정 | ✅ 완료 | 디바운스/보호 중에도 화살표 항상 표시 |
+| GREEN 안정성 | ✅ 완료 | 7초 hold + 3회 연속 실패 exit + phase 보호 |
+| IMU 모션 감지 | 🔜 예정 | vesiscanbasicAndroid에서 포팅 예정 |
 | Placement 팬텀 테스트 | 🔜 예정 | Gradient vs SWEEP 비교 |
 | 5-Anchor calibration | 🔜 검토 | CKLaw 전체 포팅 여부 결정 |
 | 인체 임상 검증 | 🔜 예정 | 상수 재조정 |
diff --git a/docs/ALGORITHM_COMPARISON.md b/docs/ALGORITHM_COMPARISON.md
new file mode 100644
index 0000000..5226373
--- /dev/null
+++ b/docs/ALGORITHM_COMPARISON.md
@@ -0,0 +1,205 @@
+# Method A / B / C Algorithm Comparison & Placement Test
+
+## Wall Detection Comparison
+
+### Pipeline
+
+```
+Method A:  raw → SG → composite(sg+|d1|+|d2|) → plateau score → plateau spans
+           → prominence wall (ANT=nearest, POST=edge_score)
+           → cross-validation → BV(frustum+ellipse cap, 1ch=sphere)
+           ※ 채널별 min_wall_contrast_ratio × cos(θ) 보정
+
+Method B:  raw → SG → TGC(multichannel log-fit) → initial detect(Otsu×0.9×cos(θ))
+           → BR candidate(per-ch, post-only, prominence≥50)
+           → consensus(median, outlier_tol=4, min_votes=3)
+           → is_reflection_only(shared+cluster, amp_ratio=1.5)
+           → resolve(suspicious post: post>ant×1.5)
+           → suppress(valley early-stop 50.0) → rerun detect
+           → choose(rerun vs initial) → BV(frustum+ellipse cap, 1ch=sphere)
+
+Method C:  raw → MedianFilter(win=7) → SG+wavelet
+           → ImpulseReject(2-pass Hampel, lumen clean)
+           → OS-CFAR(per-sample) → lumen mask
+           → prominence wall + subsample refine
+           → StaLta impulse purity check
+           → anatomical gate (antDepth≥10mm, chord 5-110mm)
+           → BModeScore V41 (wamp=0.45, stalta=0.20, far=0.15, dark=0.10)
+           → ChordConsensus (Tukey MAD + Fischler-Bolles pair test)
+           → BV dispatch(frustum/chord/sphere, trusted channels only)
+```
+
+### Stage-by-Stage
+
+| Stage | **A (Plateau)** | **B (Otsu+TGC+BR)** | **C (V4.1 CFAR)** |
+|-------|-----------------|----------------------|---------------------|
+| Pre-filter | none | none | MedianFilter(win=7) + ImpulseReject(Hampel) |
+| Denoising | SG(5,2) | SG(5,2) → log-TGC | SG(5,2) + db4 wavelet 3-level |
+| Threshold | sliding plateau score Q=0.5 | Otsu×0.9×cos(θ) | OS-CFAR (win=15, rank=40%, scale=1.05) |
+| Low-echo mask | platScore < thr | sg <= otsu (full) | sg <= median(CFAR) |
+| Span merge | gap≤5, simple | gap<3: unconditional, ≥3: wall check | mergeGapMax=5, gapPeakMargin=50 |
+| Span refine | none | refineRightEdge | none |
+| Wall select | ANT=nearest, POST=edge_score, decay=0.15 | ANT=nearest, POST=edge_score, decay=0.12 | prominence + subsample, MAX_CANDIDATES_POST=64 |
+| Valley logic | descending-first, rise=5 | descending-first, rise=50 | rise=50 |
+| Extra conditions | contrast×cos(θ)≥1.2, prom≥3 | peakMin=max(low+30,thr), sg[ant/post]≥thr, postProm≥30 | Kremkau ant fallback, antMinIdx=7 |
+| Score | sg[ant]+sg[post] | asymmetric ant_reliability | BModeScore V41 (wamp+stalta+far+dark+grad) |
+| FP filter | cross-validation | score<3000 | AnatomicalGate + ChordConsensus |
+| Impulse check | none | none | StaLta (STA/LTA ratio) |
+| Channel filter | none | none | ChordConsensus (MAD outlier + pair test) |
+| Back reflection | none | consensus multichannel BR | none |
+| Fallback | none | ant=max(0,s-(post-e)) | B-mode tier |
+
+### BV Estimation
+
+| | **A** | **B** | **C** |
+|---|---|---|---|
+| Model | shared with B | frustum + ellipse cap | Multi-dispatch (trusted ch only) |
+| 1-channel | sphere V=(4/3)πR³ | same | Verathon chord |
+| Channel filter | none | none | ChordConsensus (drop inconsistent) |
+| Cap height | 8-point ellipse LSQ | same | fixed: bottom=hemisphere, top=cone |
+| LR ratio | shared with B | 2-lateral ellipse solve + shrinkage | 1/avg_ratio, clamp[1.0,1.6] |
+| Confidence | none | none | 0.95(4C+2L) ~ 0.20(1ch) |
+| DPS | PiezoHW (1.968) | same | 1.9309 |
+
+### Angle Correction (PR#20)
+
+Both Method A and B apply per-channel beam angle correction:
+- **Method B**: `otsu_ratio = OTSU_RATIO × cos(θ)` per channel
+- **Method A**: `min_wall_contrast_ratio = 1.2 × cos(θ)` per channel
+- Larger angles → lower threshold → better detection of weak posterior walls
+
+### Back Reflection System (Method B)
+
+```
+Per-channel:
+  1. initial detect → (ant, post)
+  2. build_candidate: strongest peak AFTER post (prominence≥50)
+     - global BR ≈ post (±3) → None (no separate BR)
+     - else → strongest significant peak after post
+
+Multichannel:
+  3. consensus: median, outlier_tol=4, min_votes=3
+  4. is_reflection_only: post > ant × 1.5 (amp_ratio)
+     - Condition A: shared_idx based
+     - Condition B: post cluster based
+
+Per-channel resolve:
+  5. is_suspicious_post: post > ant × 1.5 OR post ≈ shared (±2)
+  6. select_idx → resolve → suppress(valley early-stop 50.0)
+  7. rerun detect → choose(rerun vs initial, min_gap=8)
+```
+
+### Method C V4.1 New Features (2026-05-04)
+
+```
+Pre-processing:
+  MedianFilter(win=7) → remove speckle bumps
+  ImpulseReject(2-pass Hampel) → clean 1-3 sample impulses in lumen
+
+Detection:
+  DetectLumenFirst V41_PARAMS:
+    mergeGapMax=5, gapPeakMargin=50
+    maxCandidatesPost=64, medianWin=7, antMinIdx=7
+    Kremkau half-amplitude ant fallback
+
+Quality:
+  StaLta: STA/LTA ratio → wall edge vs reverberation discrimination
+  BModeScore V41_WEIGHTS:
+    wamp=0.45 (wall-peak amplitude)
+    stalta=0.20 (impulse purity)
+    far=0.15, dark=0.10, ant=0.05, post=0.05
+
+Channel Filtering:
+  ChordConsensus: Tukey MAD outlier + Fischler-Bolles pair test
+  → drop geometrically inconsistent channels before BV
+
+Anatomical Gate:
+  antDepthMin: 22 → 10mm (Neyman-Pearson loose prior)
+  strict threshold removed → delegated to B-mode score
+```
+
+---
+
+## Python vs Kotlin Sync Status (2026-05-04)
+
+### Method A/B: 18 functions compared — CRITICAL 0, MINOR 5
+
+All config constants match: LOW_ECHO_AMP=1250, OTSU_RATIO=0.9, MIN_SCORE=3000,
+EDGE_DIST_DECAY=0.12, VALLEY_STOP_RISE=50, etc.
+
+### Method C: Direct copy from CharlesKWONsLaw (45 files, package renamed)
+
+---
+
+## Placement Test Algorithm
+
+### Overview (2026-05-11 updated)
+
+```
+Screen entry → "Place VesiScan above the pubic bone, then press Start"
+    ↓ Start Alignment 버튼 탭 (waitingForStart=false)
+전체 상태 리셋
+    ↓
+[1-second interval loop]
+    ↓
+mpa (first time, 500ms delay) → maa → 6ch reb
+    ↓
+Detachment check (6ch received, THR=30) → LED 4 if detached
+    ↓
+Wall detection (Method A/B/C) → urineLen ≥ 12
+    ↓
+computePlacementGuide() → 3-stage guide (VERTICAL → LATERAL → GREEN)
+    ↓
+Debounce (2 consecutive + 1.5s/3s hold) + Phase protection (3 scans)
+    ↓
+Arrow direction: always updated (directionIcon synced with guideResult)
+    ↓
+LED: stage change only (4=detach, 5=searching, 6=complete)
+    ↓
+GREEN: 7s hold + 3 consecutive fail to exit
+    ↓
+Screen exit → LED OFF
+```
+
+### Guide Modes
+
+**Gradient** (default): weighted center gradient → LATERAL → GREEN
+**Boundary**: up → detect boundary (max drops) → come back → LATERAL
+**SWEEP** (CKLaw): navel → slide down → sagittalArgMaxCh → LATERAL → GREEN
+
+### 3-Stage Guide
+
+**Stage 1 VERTICAL**: detect count + gradient + "Slide up/down ↑↓"
+**Stage 2 LATERAL**: |len4-len5| ≤ 10 → GREEN, else "Slide left/right ←→"
+**Stage 3 GREEN**: CV ≤ threshold AND |LR dev| ≤ 0.20 → "In position!" (7s hold)
+
+### Measurement Modes
+
+- **Auto Scan**: min 800ms gap, 10-sample trimmed mean (max/min removed, 8 avg)
+- **Single Scan (Spot)**: 5회 측정 → trimmed mean (max 8 attempts, min 3)
+- valid ≥ 4 channels only
+- Analysis on coroutine (Dispatchers.Default)
+- Auto fail: 2ch+ missing 5 consecutive → realign dialog
+- Detachment → LED 4 (once), recovery → LED 0 (once)
+- Foreground Service: BLE connection maintained during screen off
+- BLE 로그: 실시간 파일 기록 (Downloads/VesiScan_BLE_*.log, 화면 잠금에도 보존)
+- CSV: 세션별 파일 (YYYY-MM-DD_HHmmss.csv)
+
+### Placement GREEN 기준
+
+```
+CV threshold = DEFAULT_CV_THR + (scanCount / 5) × 0.03
+  DEFAULT_CV_THR: V0=0.07, V1/V2=0.10, 기타=0.08
+LR deviation ≤ 0.20
+GREEN hold: 7초 (greenLockedAtMs 기준)
+GREEN exit: 3회 연속 실패 (greenFailCount)
+```
+
+### Test Results (2026-05-04, 500ml phantom, Method C V4.1)
+
+```
+총 측정: 223회
+평균: 492.4ml (오차 -1.5%)
+±15% 이내: 223/223 (100%)
+범위: 441~537ml
+```