added marker lines

HOWTO.md

@@ -404,7 +404,9 @@ samples existed before the RRD was created.
 
 Temperature uses the left axis with a default range of 0–30°C. Humidity and
 battery use the right axis with a default range of 0–100%. These ranges and
-labels can be changed in `config.yaml` under `graph.axes`.
+labels can be changed in `config.yaml` under `graph.axes`. Light-grey reference
+lines are drawn at 15, 20, and 25°C by default and can be changed under
+`graph.axes.temperature.reference_lines`.
 
 The collector also generates `/var/www/html/sensors/index.html`. It displays
 six graphs at a time and has controls for switching between the daily, monthly,
@@ -442,9 +444,9 @@ To run it automatically as a user service, copy the supplied service file. It
 assumes this repository is located at `$HOME/service_zigbee`:
 
 ```bash
-cp zigbee-sensor.service.example /etc/systemd/system
-systemctl --user daemon-reload
-systemctl --user enable --now zigbee-sensor.service
+cp zigbee-sensors.service.example /etc/systemd/system
+systemctl daemon-reload
+systemctl enable --now zigbee-sensors.service
 ```
 
 Inspect its status and live logs with:

config.yaml

@@ -78,6 +78,13 @@ graph:
       minimum: 0
       maximum: 30
       label: degrees C
+      reference_lines:
+        - value: 15
+          color: D3D3D3
+        - value: 20
+          color: D3D3D3
+        - value: 25
+          color: D3D3D3
     percentage:
       minimum: 0
       maximum: 100

read_temperature.py

@@ -211,6 +211,10 @@ def render_graphs(sensor: Sensor, rrd_path: Path, config: Config) -> None:
     percentage_transform = (
         f"{percentage_minimum},-,{percentage_to_temperature},*,{temperature_minimum},+"
     )
+    reference_lines = [
+        f"HRULE:{float(line['value'])}#{line['color']}"
+        for line in temperature_axis.get("reference_lines", [])
+    ]
     optional_flags = []
     if graph.get("slope_mode", False):
         optional_flags.append("--slope-mode")
@@ -235,6 +239,7 @@ def render_graphs(sensor: Sensor, rrd_path: Path, config: Config) -> None:
             f"CDEF:humidity_scaled=humidity,{percentage_transform}",
             f"CDEF:battery_scaled=battery,{percentage_transform}",
             f"AREA:temp#{temperature['color']}:{temperature['legend']}",
+            *reference_lines,
             f"LINE{humidity['line_width']}:humidity_scaled#{humidity['color']}:{humidity['legend']}",
             f"LINE{battery['line_width']}:battery_scaled#{battery['color']}:{battery['legend']}:dashes={battery['dashes']}",
             f"GPRINT:temp:LAST:{temperature['last_value_format']}",