diff --git a/ecowitt2mqtt/helpers/calculator/__init__.py b/ecowitt2mqtt/helpers/calculator/__init__.py
index 4d18ffb8..4b85480a 100644
--- a/ecowitt2mqtt/helpers/calculator/__init__.py
+++ b/ecowitt2mqtt/helpers/calculator/__init__.py
@@ -7,6 +7,7 @@
 from functools import wraps
 from typing import TYPE_CHECKING, Any, Callable, Dict, TypeVar
 
+from ecowitt2mqtt.const import UNIT_SYSTEM_IMPERIAL
 from ecowitt2mqtt.errors import EcowittError
 from ecowitt2mqtt.helpers.typing import CalculatedValueType, PreCalculatedValueType
 
@@ -52,6 +53,16 @@ def __init__(self, config: Config, payload_key: str, data_point_key: str) -> Non
         self._data_point_key = data_point_key
         self._payload_key = payload_key
 
+    @property
+    def default_imperial_unit(self) -> str | None:
+        """Get the default unit (imperial)."""
+        return None
+
+    @property
+    def default_metric_unit(self) -> str | None:
+        """Get the default unit (metric)."""
+        return None
+
     @property
     def output_unit(self) -> str | None:
         """Get the output unit of measurement for this calculation."""
@@ -75,8 +86,19 @@ def get_calculated_data_point(
         data_type: DataPointType | None = None,
     ) -> CalculatedDataPoint:
         """Get the output unit for this calculation."""
+        output_unit: str | None
+
+        # If the user explicitly sets self.output_unit, use it if it's truthy;
+        # otherwise, default to the standard output unit for the unit system:
+        if self.output_unit:
+            output_unit = self.output_unit
+        elif self._config.output_unit_system == UNIT_SYSTEM_IMPERIAL:
+            output_unit = self.default_imperial_unit
+        else:
+            output_unit = self.default_metric_unit
+
         data_point = CalculatedDataPoint(
-            data_point_key=self._data_point_key, value=value, unit=self.output_unit
+            data_point_key=self._data_point_key, value=value, unit=output_unit
         )
 
         if attributes:
diff --git a/ecowitt2mqtt/helpers/calculator/humidity.py b/ecowitt2mqtt/helpers/calculator/humidity.py
index 4c9f243b..b3c43920 100644
--- a/ecowitt2mqtt/helpers/calculator/humidity.py
+++ b/ecowitt2mqtt/helpers/calculator/humidity.py
@@ -25,10 +25,13 @@ class AbsoluteHumidityCalculator(Calculator):
     """Define an absolute humidity calculator."""
 
     @property
-    def output_unit(self) -> str | None:
-        """Get the output unit of measurement for this calculation."""
-        if self._config.output_unit_system == UNIT_SYSTEM_IMPERIAL:
-            return VOLUME_POUNDS_PER_CUBIC_FOOT
+    def default_imperial_unit(self) -> str:
+        """Get the default unit (imperial)."""
+        return VOLUME_POUNDS_PER_CUBIC_FOOT
+
+    @property
+    def default_metric_unit(self) -> str:
+        """Get the default unit (metric)."""
         return VOLUME_GRAMS_PER_CUBIC_METER
 
     @Calculator.requires_keys(DATA_POINT_TEMP, DATA_POINT_HUMIDITY)
@@ -54,6 +57,11 @@ class RelativeHumidityCalculator(SimpleCalculator):
     """Define a boolean leak calculator."""
 
     @property
-    def output_unit(self) -> str | None:
-        """Get the output unit of measurement for this calculation."""
+    def default_imperial_unit(self) -> str:
+        """Get the default unit (imperial)."""
+        return PERCENTAGE
+
+    @property
+    def default_metric_unit(self) -> str:
+        """Get the default unit (metric)."""
         return PERCENTAGE
diff --git a/ecowitt2mqtt/helpers/calculator/illuminance.py b/ecowitt2mqtt/helpers/calculator/illuminance.py
index 2f460301..57cf64bb 100644
--- a/ecowitt2mqtt/helpers/calculator/illuminance.py
+++ b/ecowitt2mqtt/helpers/calculator/illuminance.py
@@ -21,8 +21,13 @@ class IlluminanceLuxCalculator(Calculator):
     """Define a illuminance calculator (lux)."""
 
     @property
-    def output_unit(self) -> str | None:
-        """Get the output unit of measurement for this calculation."""
+    def default_imperial_unit(self) -> str:
+        """Get the default unit (imperial)."""
+        return LIGHT_LUX
+
+    @property
+    def default_metric_unit(self) -> str:
+        """Get the default unit (metric)."""
         return LIGHT_LUX
 
     @Calculator.requires_keys(DATA_POINT_SOLARRADIATION)
@@ -41,8 +46,13 @@ class IlluminancePerceivedCalculator(Calculator):
     """Define a illuminance calculator (perceived)."""
 
     @property
-    def output_unit(self) -> str | None:
-        """Get the output unit of measurement for this calculation."""
+    def default_imperial_unit(self) -> str:
+        """Get the default unit (imperial)."""
+        return PERCENTAGE
+
+    @property
+    def default_metric_unit(self) -> str:
+        """Get the default unit (metric)."""
         return PERCENTAGE
 
     @Calculator.requires_keys(DATA_POINT_SOLARRADIATION)
@@ -68,6 +78,11 @@ class IlluminanceWM2Calculator(SimpleCalculator):
     """Define a illuminance calculator (W/m²)."""
 
     @property
-    def output_unit(self) -> str | None:
-        """Get the output unit of measurement for this calculation."""
+    def default_imperial_unit(self) -> str:
+        """Get the default unit (imperial)."""
+        return ILLUMINANCE_WATTS_PER_SQUARE_METER
+
+    @property
+    def default_metric_unit(self) -> str:
+        """Get the default unit (metric)."""
         return ILLUMINANCE_WATTS_PER_SQUARE_METER
diff --git a/ecowitt2mqtt/helpers/calculator/lightning.py b/ecowitt2mqtt/helpers/calculator/lightning.py
index 1e3f3c08..12649d52 100644
--- a/ecowitt2mqtt/helpers/calculator/lightning.py
+++ b/ecowitt2mqtt/helpers/calculator/lightning.py
@@ -6,7 +6,6 @@
     LENGTH_MILES,
     LOGGER,
     STRIKES,
-    UNIT_SYSTEM_IMPERIAL,
     UNIT_SYSTEM_METRIC,
 )
 from ecowitt2mqtt.helpers.calculator import (
@@ -21,8 +20,13 @@ class LightningStrikeCountCalculator(SimpleCalculator):
     """Define a lightning strike count calculator."""
 
     @property
-    def output_unit(self) -> str | None:
-        """Get the output unit of measurement for this calculation."""
+    def default_imperial_unit(self) -> str:
+        """Get the default unit (imperial)."""
+        return STRIKES
+
+    @property
+    def default_metric_unit(self) -> str:
+        """Get the default unit (metric)."""
         return STRIKES
 
 
@@ -33,10 +37,13 @@ class LightningStrikeDistanceCalculator(Calculator):
     """
 
     @property
-    def output_unit(self) -> str | None:
-        """Get the output unit of measurement for this calculation."""
-        if self._config.output_unit_system == UNIT_SYSTEM_IMPERIAL:
-            return LENGTH_MILES
+    def default_imperial_unit(self) -> str:
+        """Get the default unit (imperial)."""
+        return LENGTH_MILES
+
+    @property
+    def default_metric_unit(self) -> str:
+        """Get the default unit (metric)."""
         return LENGTH_KILOMETERS
 
     def calculate_from_value(
diff --git a/ecowitt2mqtt/helpers/calculator/precipitation.py b/ecowitt2mqtt/helpers/calculator/precipitation.py
index 3b69823f..b4686a8b 100644
--- a/ecowitt2mqtt/helpers/calculator/precipitation.py
+++ b/ecowitt2mqtt/helpers/calculator/precipitation.py
@@ -16,10 +16,13 @@ class RainRateCalculator(Calculator):
     """Define a rain rate calculator."""
 
     @property
-    def output_unit(self) -> str | None:
-        """Get the output unit of measurement for this calculation."""
-        if self._config.output_unit_system == UNIT_SYSTEM_IMPERIAL:
-            return PRECIPITATION_INCHES_PER_HOUR
+    def default_imperial_unit(self) -> str:
+        """Get the default unit (imperial)."""
+        return PRECIPITATION_INCHES_PER_HOUR
+
+    @property
+    def default_metric_unit(self) -> str:
+        """Get the default unit (metric)."""
         return PRECIPITATION_MILLIMETERS_PER_HOUR
 
     def calculate_from_value(
@@ -41,10 +44,13 @@ class RainVolumeCalculator(Calculator):
     """Define a rain volume calculator."""
 
     @property
-    def output_unit(self) -> str | None:
-        """Get the output unit of measurement for this calculation."""
-        if self._config.output_unit_system == UNIT_SYSTEM_IMPERIAL:
-            return PRECIPITATION_INCHES
+    def default_imperial_unit(self) -> str:
+        """Get the default unit (imperial)."""
+        return PRECIPITATION_INCHES
+
+    @property
+    def default_metric_unit(self) -> str:
+        """Get the default unit (metric)."""
         return PRECIPITATION_MILLIMETERS
 
     def calculate_from_value(
diff --git a/ecowitt2mqtt/helpers/calculator/pressure.py b/ecowitt2mqtt/helpers/calculator/pressure.py
index 59509a79..d3604c50 100644
--- a/ecowitt2mqtt/helpers/calculator/pressure.py
+++ b/ecowitt2mqtt/helpers/calculator/pressure.py
@@ -10,10 +10,13 @@ class PressureCalculator(Calculator):
     """Define a pressure calculator."""
 
     @property
-    def output_unit(self) -> str | None:
-        """Get the output unit of measurement for this calculation."""
-        if self._config.output_unit_system == UNIT_SYSTEM_IMPERIAL:
-            return PRESSURE_INHG
+    def default_imperial_unit(self) -> str:
+        """Get the default unit (imperial)."""
+        return PRESSURE_INHG
+
+    @property
+    def default_metric_unit(self) -> str:
+        """Get the default unit (metric)."""
         return PRESSURE_HPA
 
     def calculate_from_value(
diff --git a/ecowitt2mqtt/helpers/calculator/temperature.py b/ecowitt2mqtt/helpers/calculator/temperature.py
index 263e0968..6bc9bd0c 100644
--- a/ecowitt2mqtt/helpers/calculator/temperature.py
+++ b/ecowitt2mqtt/helpers/calculator/temperature.py
@@ -177,10 +177,13 @@ class TemperatureUnitConverter(Calculator):
     """Define a base temperature calculator."""
 
     @property
-    def output_unit(self) -> str | None:
-        """Get the output unit of measurement for this calculation."""
-        if self._config.output_unit_system == UNIT_SYSTEM_IMPERIAL:
-            return TEMP_FAHRENHEIT
+    def default_imperial_unit(self) -> str:
+        """Get the default unit (imperial)."""
+        return TEMP_FAHRENHEIT
+
+    @property
+    def default_metric_unit(self) -> str:
+        """Get the default unit (metric)."""
         return TEMP_CELSIUS
 
 
diff --git a/ecowitt2mqtt/helpers/calculator/time.py b/ecowitt2mqtt/helpers/calculator/time.py
index 613e01a9..68e2d172 100644
--- a/ecowitt2mqtt/helpers/calculator/time.py
+++ b/ecowitt2mqtt/helpers/calculator/time.py
@@ -31,6 +31,11 @@ class RuntimeCalculator(SimpleCalculator):
     """Define a runtime calculator."""
 
     @property
-    def output_unit(self) -> str | None:
-        """Get the output unit of measurement for this calculation."""
+    def default_imperial_unit(self) -> str:
+        """Get the default unit (imperial)."""
+        return TIME_SECONDS
+
+    @property
+    def default_metric_unit(self) -> str:
+        """Get the default unit (metric)."""
         return TIME_SECONDS
diff --git a/ecowitt2mqtt/helpers/calculator/uv.py b/ecowitt2mqtt/helpers/calculator/uv.py
index 4333e0ec..178e9133 100644
--- a/ecowitt2mqtt/helpers/calculator/uv.py
+++ b/ecowitt2mqtt/helpers/calculator/uv.py
@@ -87,8 +87,13 @@ class SafeExposureCalculator(Calculator):
     """Define a safe exposure calculator."""
 
     @property
-    def output_unit(self) -> str | None:
-        """Get the output unit of measurement for this calculation."""
+    def default_imperial_unit(self) -> str:
+        """Get the default unit (imperial)."""
+        return TIME_MINUTES
+
+    @property
+    def default_metric_unit(self) -> str:
+        """Get the default unit (metric)."""
         return TIME_MINUTES
 
     @Calculator.requires_keys(DATA_POINT_UV)
@@ -126,6 +131,11 @@ class UVIndexCalculator(SimpleCalculator):
     """Define a UV index calculator."""
 
     @property
-    def output_unit(self) -> str | None:
-        """Get the output unit of measurement for this calculation."""
+    def default_imperial_unit(self) -> str:
+        """Get the default unit (imperial)."""
+        return UV_INDEX
+
+    @property
+    def default_metric_unit(self) -> str:
+        """Get the default unit (metric)."""
         return UV_INDEX
diff --git a/ecowitt2mqtt/helpers/calculator/wind.py b/ecowitt2mqtt/helpers/calculator/wind.py
index 186ec143..809b0479 100644
--- a/ecowitt2mqtt/helpers/calculator/wind.py
+++ b/ecowitt2mqtt/helpers/calculator/wind.py
@@ -255,8 +255,13 @@ class WindDirCalculator(SimpleCalculator):
     """Define a wind direction calculator."""
 
     @property
-    def output_unit(self) -> str | None:
-        """Get the output unit of measurement for this calculation."""
+    def default_imperial_unit(self) -> str:
+        """Get the default unit (imperial)."""
+        return DEGREE
+
+    @property
+    def default_metric_unit(self) -> str:
+        """Get the default unit (metric)."""
         return DEGREE
 
 
@@ -264,10 +269,13 @@ class WindSpeedCalculator(Calculator):
     """Define a wind speed calculator."""
 
     @property
-    def output_unit(self) -> str | None:
-        """Get the output unit of measurement for this calculation."""
-        if self._config.output_unit_system == UNIT_SYSTEM_IMPERIAL:
-            return SPEED_MILES_PER_HOUR
+    def default_imperial_unit(self) -> str:
+        """Get the default unit (imperial)."""
+        return SPEED_MILES_PER_HOUR
+
+    @property
+    def default_metric_unit(self) -> str:
+        """Get the default unit (metric)."""
         return SPEED_KILOMETERS_PER_HOUR
 
     def calculate_from_value(