Improve example in SCD4X for ambient pressure compensation (#2645)

* Update scd4x.rst

* Update scd4x.rst

* Update scd4x.rst

* Improve calibration example

components/sensor/scd4x.rst

@@ -105,14 +105,18 @@ As of April 2022 the average fresh air Co² concentration is 419 ppm.
             value: 419   # outside average April 2022
             id: my_scd41
 
-value can be a template
+value can also be a template, for example to define a Home Assistant calibration service:
 
 .. code-block:: yaml
 
-    on_...:
+    api:
+      services:
+        - service: calibrate_co2_value
+          variables:
+            co2_ppm: int
           then:
-        - scd4x._perform_forced_calibration_action:
-            value: !lambda "{ return 419 };"
+          - scd4x.perform_forced_calibration:
+              value: !lambda 'return co2_ppm;'
               id: my_scd41
 
 
@@ -129,39 +133,53 @@ This :ref:`action <config-action>` triggers a factory reset of the sensor. Calib
       then:
         - scd4x.factory_reset: my_scd41
 
-Automation
------------------
+Pressure compensation
+---------------------
 
-Ambient pressure compensation compensation can be changed from :ref:`lambdas <config-lambda>`
+A static ambient pressure value can be set with `ambient_pressure_compensation` or `altitude_compensation`. It can also be changed dynamically with :ref:`lambdas <config-lambda>` using `set_ambient_pressure_compensation(<mBar>)`, or by pointing `ambient_pressure_compensation_source` to a local pressure sensor.
 
+Example with a local sensor
+***************************
 
-``set_ambient_pressure_compensation(  <pressure in bar)``
-
-
-
-Example
-*******
-
-Note: that the pressure from bme280 is in hPa and must be converted to bar.
+Note: remember your pressure sensor needs to output in mBar
 
 .. code-block:: yaml
 
     sensor:
-      - platform: scd4x
-        id: scd41
-        i2c_id: bus_a
-        co2:
-            name: co2
-            id: co2
-
       - platform: bme280
         pressure:
-            name: "BME280-Pressure"
-            id: bme280_pressure
-            oversampling: 1x
-          on_value:
+          name: "Ambient Pressure"
+          id: bme_pressure
+
+      - platform: scd4x
+        measurement_mode: low_power_periodic
+        ambient_pressure_compensation_source: bme_pressure
+        temperature_offset: 0
+        co2:
+          name: "CO2 level"
+
+Example with a remote sensor
+****************************
+
+This example creates a service `set_ambient_pressure` that can be called from Home Assistant:
+
+.. code-block:: yaml
+
+    api:
+      services:
+        - service: set_ambient_pressure
+          variables:
+            pressure_mbar: int
           then:
-                - lambda: "id(scd41)->set_ambient_pressure_compensation(x / 1000.0);"
+            - lambda: "id(my_scd41)->set_ambient_pressure_compensation(pressure_mbar);"
+
+    sensor:
+      - platform: scd4x
+        id: my_scd41
+        measurement_mode: low_power_periodic
+        temperature_offset: 0
+        co2:
+          name: "CO2 level"
 
 
 See Also