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app/web.py

@@ -22,6 +22,10 @@ def create_app() -> Flask:
     app.secret_key = config.flask_secret_key
     init_db()
 
+    @app.context_processor
+    def inject_common_template_vars() -> dict[str, int]:
+        return {"collect_interval_seconds": config.collect_interval_seconds}
+
     @app.get("/")
     def dashboard() -> str:
         tz = ZoneInfo(config.app_timezone)
@@ -43,10 +47,10 @@ def create_app() -> Flask:
             "dashboard.html",
             devices=devices,
             latest=latest,
+            latest_relative=latest_ages_for_display(latest, tz),
             stats=stats_by_device(readings),
             chart_json=json.dumps(chart_payload(readings, tz)),
             timezone=config.app_timezone,
-            collect_interval_seconds=config.collect_interval_seconds,
         )
 
     @app.get("/devices/<device_id>")
@@ -262,6 +266,34 @@ def readings_for_display(readings: list[Reading], tz: ZoneInfo) -> list[dict[str
     return rows
 
 
+def latest_ages_for_display(latest: dict[str, Reading], tz: ZoneInfo) -> dict[str, str]:
+    now_local = datetime.now(tz)
+    ages: dict[str, str] = {}
+
+    for device_id, reading in latest.items():
+        collected_local = reading.recorded_at.replace(tzinfo=timezone.utc).astimezone(tz)
+        delta_seconds = max(0, int((now_local - collected_local).total_seconds()))
+
+        if delta_seconds < 60:
+            ages[device_id] = "just now"
+            continue
+
+        minutes = delta_seconds // 60
+        if minutes < 60:
+            ages[device_id] = f"{minutes} min ago"
+            continue
+
+        hours = minutes // 60
+        if hours < 24:
+            ages[device_id] = f"{hours} h ago"
+            continue
+
+        days = hours // 24
+        ages[device_id] = f"{days} d ago"
+
+    return ages
+
+
 def report_rows(
     session: Session,
     start_utc: datetime,