diff --git a/lib/l10n/app_de.arb b/lib/l10n/app_de.arb
index 88221f1f8..955ae3af3 100644
--- a/lib/l10n/app_de.arb
+++ b/lib/l10n/app_de.arb
@@ -1352,8 +1352,8 @@
   "healthCatMovementLoad": "Bewegung & Belastung",
   "healthCatBodyWear": "Körper & Tragezeit",
   "healthBlurbRestingHr": "Der niedrigste anhaltende Puls der Nacht",
-  "healthBlurbHrv": "RMSSD im saubersten Schlafabschnitt",
-  "healthBlurbHrvCv": "Wie stark das von Nacht zu Nacht schwankt",
+  "healthBlurbHrv": "Mittlerer RMSSD über die 5-Minuten-Fenster der Nacht",
+  "healthBlurbHrvCv": "SDNN als Anteil des mittleren Schlagintervalls, innerhalb einer Nacht",
   "healthBlurbLfHf": "Wie sich die Herzschlag-Variabilität auf die Frequenzbereiche verteilt",
   "healthBlurbDip": "Wie stark deine Herzfrequenz im Schlaf sinkt",
   "healthBlurbHrr": "Wie schnell sie in der Minute nach einer Belastung sinkt",
diff --git a/lib/l10n/app_en.arb b/lib/l10n/app_en.arb
index 874abe33f..756a7765d 100644
--- a/lib/l10n/app_en.arb
+++ b/lib/l10n/app_en.arb
@@ -6737,13 +6737,13 @@
   "@healthBlurbRestingHr": {
     "description": "Explore catalogue one-line description for resting heart rate"
   },
-  "healthBlurbHrv": "RMSSD over the cleanest window of sleep",
+  "healthBlurbHrv": "Mean RMSSD across the night's 5-minute windows",
   "@healthBlurbHrv": {
-    "description": "Explore catalogue one-line description for HRV"
+    "description": "Explore catalogue one-line description for HRV: the nightly mean of the RMSSDs of the sleep session's 5-minute windows"
   },
-  "healthBlurbHrvCv": "How much that swings from night to night",
+  "healthBlurbHrvCv": "SDNN as a share of the average beat interval, within one night",
   "@healthBlurbHrvCv": {
-    "description": "Explore catalogue one-line description for HRV night-to-night variability"
+    "description": "Explore catalogue one-line description for HRV stability: within-night SDNN as a percentage of the mean beat interval (not a night-to-night variability)"
   },
   "healthBlurbLfHf": "Where beat-timing power sits across frequencies",
   "@healthBlurbLfHf": {
diff --git a/lib/l10n/app_es.arb b/lib/l10n/app_es.arb
index 5efd2cb99..c81fd67bf 100644
--- a/lib/l10n/app_es.arb
+++ b/lib/l10n/app_es.arb
@@ -1308,8 +1308,8 @@
   "healthCatMovementLoad": "Movimiento y carga",
   "healthCatBodyWear": "Cuerpo y uso",
   "healthBlurbRestingHr": "El ritmo sostenido más bajo de la noche",
-  "healthBlurbHrv": "RMSSD durante la ventana de sueño más limpia",
-  "healthBlurbHrvCv": "Cuánto varía eso de una noche a otra",
+  "healthBlurbHrv": "RMSSD medio de las ventanas de 5 minutos de la noche",
+  "healthBlurbHrvCv": "SDNN como fracción del intervalo medio entre latidos, dentro de una noche",
   "healthBlurbLfHf": "Dónde se concentra la potencia del ritmo cardíaco entre frecuencias",
   "healthBlurbDip": "Cuánto baja tu frecuencia cardíaca mientras duermes",
   "healthBlurbHrr": "Cuán rápido baja en el minuto después de un esfuerzo",
diff --git a/lib/l10n/app_fr.arb b/lib/l10n/app_fr.arb
index 0968ca11f..e91fb62f9 100644
--- a/lib/l10n/app_fr.arb
+++ b/lib/l10n/app_fr.arb
@@ -1308,8 +1308,8 @@
   "healthCatMovementLoad": "Mouvement et charge",
   "healthCatBodyWear": "Corps et port",
   "healthBlurbRestingHr": "Le rythme soutenu le plus bas de la nuit",
-  "healthBlurbHrv": "RMSSD sur la fenêtre de sommeil la plus propre",
-  "healthBlurbHrvCv": "À quel point cela varie d'une nuit à l'autre",
+  "healthBlurbHrv": "RMSSD moyen sur les fenêtres de 5 minutes de la nuit",
+  "healthBlurbHrvCv": "SDNN en proportion de l'intervalle moyen entre battements, sur une nuit",
   "healthBlurbLfHf": "Où se situe la puissance du rythme cardiaque selon les fréquences",
   "healthBlurbDip": "De combien votre fréquence cardiaque baisse pendant votre sommeil",
   "healthBlurbHrr": "À quelle vitesse elle baisse dans la minute suivant un effort",
diff --git a/lib/l10n/app_hi.arb b/lib/l10n/app_hi.arb
index 2d63f9052..d2b467e9b 100644
--- a/lib/l10n/app_hi.arb
+++ b/lib/l10n/app_hi.arb
@@ -1308,8 +1308,8 @@
   "healthCatMovementLoad": "गतिविधि और भार",
   "healthCatBodyWear": "शरीर और पहनावा",
   "healthBlurbRestingHr": "रात की सबसे कम स्थिर दर",
-  "healthBlurbHrv": "नींद के सबसे स्वच्छ समय-खंड पर RMSSD",
-  "healthBlurbHrvCv": "यह रात-दर-रात कितना बदलता है",
+  "healthBlurbHrv": "रात की 5-मिनट की खिड़कियों पर औसत RMSSD",
+  "healthBlurbHrvCv": "एक रात के भीतर, औसत धड़कन-अंतराल के अनुपात में SDNN",
   "healthBlurbLfHf": "धड़कन-समय की ऊर्जा विभिन्न आवृत्तियों में कहाँ है",
   "healthBlurbDip": "सोते समय आपकी हृदय गति कितनी गिरती है",
   "healthBlurbHrr": "किसी कसरत के बाद एक मिनट में यह कितनी तेज़ी से गिरती है",
diff --git a/lib/l10n/app_zh.arb b/lib/l10n/app_zh.arb
index 33a526376..5362014c5 100644
--- a/lib/l10n/app_zh.arb
+++ b/lib/l10n/app_zh.arb
@@ -1308,8 +1308,8 @@
   "healthCatMovementLoad": "运动与负荷",
   "healthCatBodyWear": "身体与佩戴",
   "healthBlurbRestingHr": "整夜持续保持的最低心率",
-  "healthBlurbHrv": "取睡眠中信号最干净时段的 RMSSD",
-  "healthBlurbHrvCv": "该数值在各夜之间的波动幅度",
+  "healthBlurbHrv": "整晚各 5 分钟窗口 RMSSD 的平均值",
+  "healthBlurbHrvCv": "单晚内 SDNN 占平均心跳间期的比例",
   "healthBlurbLfHf": "心跳间期功率在各频段的分布",
   "healthBlurbDip": "睡眠期间心率下降的幅度",
   "healthBlurbHrr": "运动结束后一分钟内心率下降的速度",
diff --git a/lib/ui2/screens/health_screen.dart b/lib/ui2/screens/health_screen.dart
index 213bdd3bd..cb5e2958a 100644
--- a/lib/ui2/screens/health_screen.dart
+++ b/lib/ui2/screens/health_screen.dart
@@ -357,8 +357,9 @@ class _Cat {
 const _catalogue = <_Cat>[
   _Cat('Heart & rhythm', [
     _CatRow('resting_hr', 'rhr', 'The lowest sustained rate of the night'),
-    _CatRow('hrv', 'rmssd', 'RMSSD over the cleanest window of sleep'),
-    _CatRow('hrv_cv', 'hrv_cv', 'How much that swings from night to night'),
+    _CatRow('hrv', 'rmssd', 'Mean RMSSD across the night\'s 5-minute windows'),
+    _CatRow('hrv_cv', 'hrv_cv',
+        'SDNN as a share of the average beat interval, within one night'),
     _CatRow('lf_hf', 'lf_hf', 'Where beat-timing power sits across frequencies'),
     _CatRow('dip', 'dip_pct', 'How far your heart rate falls while you sleep'),
     _CatRow('hrr', 'hrr_bpm', 'How fast it falls in the minute after a bout'),
diff --git a/lib/ui2/screens/metric_detail.dart b/lib/ui2/screens/metric_detail.dart
index 842b1ed70..a99fddeae 100644
--- a/lib/ui2/screens/metric_detail.dart
+++ b/lib/ui2/screens/metric_detail.dart
@@ -115,11 +115,15 @@ const _specs = <String, MetricSpec>{
     unit: 'ms',
     color: C.green,
     icon: LucideIcons.activity,
-    method: 'RMSSD over the longest artefact-free window during sleep. Beat '
-        'timing is recovered from the band\'s 1 Hz records and corrected by '
-        'the Lipponen–Tarvainen method before any statistic is taken. '
+    method: 'The mean of RMSSD across every 5-minute window of the detected '
+        'sleep session that holds at least 20 clean successive differences. '
+        'Beats outside 300–2000 ms, and beats more than 20% from their local '
+        'median, are dropped first. On a night whose beat timing looks noisy, '
+        'only windows that pass the jitter check on their own, or that sit on '
+        'a steady breathing line, count; a window, or a night, whose beats '
+        'add up to more time than passed is left out. '
         'Pulse-derived, so this is PRV: real and trendable, but not ECG HRV.',
-    citation: 'Task Force 1996 · Lipponen & Tarvainen 2019',
+    citation: 'Task Force 1996 · 20% local-median ectopic filter, after Malik',
     requires: {InputSignal.rrIntervals},
   ),
   'readiness': MetricSpec(
@@ -301,8 +305,12 @@ const _specs = <String, MetricSpec>{
     color: C.green,
     icon: LucideIcons.activity,
     higherBetter: false,
-    method: 'Night-to-night coefficient of variation of RMSSD.',
-    citation: 'Within-user dispersion',
+    method: 'Within one night: the standard deviation of the night\'s beat '
+        'intervals after artifact correction (SDNN) as a percentage of their '
+        'mean. The chart shows how that per-night figure moves across nights; '
+        'it is not a night-to-night coefficient of variation.',
+    citation: 'SDNN (Task Force 1996) over Lipponen & Tarvainen 2019 corrected '
+        'beats, normalised by mean NN',
     requires: {InputSignal.rrIntervals},
   ),
   'brv': MetricSpec(