diff --git a/docs/user-guide/plotting.qmd b/docs/user-guide/plotting.qmd
index 5fdce145d..ca364d885 100644
--- a/docs/user-guide/plotting.qmd
+++ b/docs/user-guide/plotting.qmd
@@ -71,6 +71,13 @@ cmp.plot.timeseries();
 cmp.plot.scatter();
 ```
 
+## Transform values
+```{python}
+(cmp.transform_values(lambda x: x / 100.0, new_quantity=ms.Quantity(cmp.quantity.name, "cm"))
+     .plot.timeseries()
+);
+```
+
 
 ## Taylor diagrams
 
diff --git a/src/modelskill/comparison/_collection.py b/src/modelskill/comparison/_collection.py
index 2e3bddf1c..7eb1e2121 100644
--- a/src/modelskill/comparison/_collection.py
+++ b/src/modelskill/comparison/_collection.py
@@ -16,6 +16,7 @@
     overload,
     Hashable,
     Tuple,
+    TYPE_CHECKING,
 )
 import zipfile
 import numpy as np
@@ -38,6 +39,10 @@
     IdxOrNameTypes,
     TimeTypes,
 )
+from ..quantity import Quantity
+
+if TYPE_CHECKING:
+    from numpy._typing._array_like import NDArray
 
 
 class ComparerCollection(Mapping):
@@ -875,3 +880,27 @@ def _load_comparer(folder: str, f: str) -> Comparer:
         cmp = Comparer.load(f)
         os.remove(f)
         return cmp
+
+    def transform_values(
+        self,
+        func: Callable[[NDArray[np.floating]], NDArray[np.floating]],
+        new_quantity: Quantity | None = None,
+    ) -> "ComparerCollection":
+        """Transform the values of all comparers using a function.
+
+        Parameters
+        ----------
+        func : Callable
+            Function to apply to the values.
+        new_quantity : Quantity, optional
+            New quantity for the transformed values. If None, the original quantity is used.
+
+        Returns
+        -------
+        ComparerCollection
+            New ComparerCollection with transformed values.
+        """
+        cmps = [
+            cmp.transform_values(func=func, new_quantity=new_quantity) for cmp in self
+        ]
+        return ComparerCollection(cmps)
diff --git a/src/modelskill/comparison/_comparison.py b/src/modelskill/comparison/_comparison.py
index eff157a34..151188c44 100644
--- a/src/modelskill/comparison/_comparison.py
+++ b/src/modelskill/comparison/_comparison.py
@@ -44,6 +44,7 @@
 
 if TYPE_CHECKING:
     from ._collection import ComparerCollection
+    from numpy._typing._array_like import NDArray
 
 Serializable = Union[str, int, float]
 
@@ -1273,3 +1274,35 @@ def load(filename: Union[str, Path]) -> "Comparer":
 
         else:
             raise NotImplementedError(f"Unknown gtype: {data.gtype}")
+
+    def transform_values(
+        self,
+        func: Callable[[NDArray[np.floating]], NDArray[np.floating]],
+        new_quantity: Quantity | None = None,
+    ) -> Comparer:
+        """Transform observation and model values using a function
+
+        Parameters
+        ----------
+        func : Callable[NDArray[np.floating]], NDArray[np.floating]]
+            function to apply to observation and model values
+        new_quantity : Quantity, optional
+            new quantity, by default None
+
+        Returns
+        -------
+        Comparer
+            new Comparer with transformed values
+
+        """
+        cmp = self.copy()
+        for var in cmp.data.data_vars:
+            if cmp.data[var].attrs["kind"] in ["observation", "model"]:
+                cmp.data[var].values = func(cmp.data[var].values)
+        for var, ts in cmp.raw_mod_data.items():
+            ts.data[var].values = func(ts.data[var].values)
+            cmp.raw_mod_data[var] = ts
+
+        if new_quantity is not None:
+            cmp.quantity = new_quantity
+        return cmp
diff --git a/tests/test_comparer.py b/tests/test_comparer.py
index 5e27818a9..dc712f30c 100644
--- a/tests/test_comparer.py
+++ b/tests/test_comparer.py
@@ -990,3 +990,23 @@ def test_load_comparer_from_root_namespace(pt_df, tmp_path):
     assert cmp2.n_points == 6
     assert cmp2.name == "Observation"
     assert cmp2.score()["m1"] == pytest.approx(0.5916079783099617)
+
+
+def test_transform_values_new_quantity(pc: Comparer) -> None:
+    assert pc.data.m1.values[0] == 1.5
+    assert pc.data.Observation.values[0] == 1.0
+    pc2 = pc.transform_values(lambda x: x / 100.0, ms.Quantity(pc.quantity.name, "cm"))
+    assert pc2.quantity.unit == "cm"
+    assert pc.data.m1.values[0] == 1.5
+    assert pc2.data.m1.values[0] == 0.015
+    assert pc.data.Observation.values[0] == 1.0
+    assert pc2.data.Observation.values[0] == 0.01
+
+
+def test_transform_values_keep_quantity(pc: Comparer) -> None:
+    pc2 = pc.transform_values(lambda x: x + 1.0)
+    assert pc2.quantity.unit == "m"
+    assert pc.data.m1.values[0] == 1.5
+    assert pc2.data.m1.values[0] == 2.5
+    assert pc.data.Observation.values[0] == 1.0
+    assert pc2.data.Observation.values[0] == 2.0
diff --git a/tests/test_comparercollection.py b/tests/test_comparercollection.py
index 85587979c..5b5806def 100644
--- a/tests/test_comparercollection.py
+++ b/tests/test_comparercollection.py
@@ -670,3 +670,10 @@ def test_score_changes_when_weights_override_defaults():
     assert cc.score()["m"] == pytest.approx(1.90909)
     assert cc.score(weights={"bar": 2.0})["m"] == pytest.approx(1.8333333)
     assert cc.score(weights={"foo": 1.0, "bar": 2.0})["m"] == pytest.approx(1.333333)
+
+
+def test_transform_values_new_quantity(cc: ms.ComparerCollection) -> None:
+    cc2 = cc.transform_values(
+        lambda x: x / 100.0, ms.Quantity(cc[0].quantity.name, "cm")
+    )
+    assert all(cmp.quantity.unit == "cm" for cmp in cc2)