Update src/CSET/operators/plot.py

Co-authored-by: James Frost <james.frost@metoffice.gov.uk>

Author: Sylviabohnenstengel

src/CSET/operators/plot.py

@@ -959,11 +959,11 @@ def _convert_precipitation_units_callback(cube: iris.cube.Cube):
     if cube.long_name == "surface_microphysical_rainfall_rate":
         if cube.units == "kg m-2 s-1":
             logging.info("Converting precipitation units from kg m-2 s-1 to mm hr-1")
-            # manually convert from kg m-2 s-1 to mm hr-1 assuming 1kg water = 1l water = 1dm^3 water
-            cube.data = cube.data * 3600.0
-
-            # update the units
-            cube.units = "mm hr-1"
+            # Convert from kg m-2 s-1 to mm s-1 assuming 1kg water = 1l water = 1dm^3 water.
+            # This is a 1:1 conversion, so we just change the units.
+            cube.units = "mm s-1"
+            # Convert the units to per hour.
+            cube.convert_units("mm hr-1")
         else:
             logging.warning(
                 "Precipitation units are not in 'kg m-2 s-1', skipping conversion"