diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 569022b7..d8bf41cb 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -20,6 +20,8 @@ Changed
 * Requiring netcdf4 >= 1.6.4
 * Optional dependencies of xarray that improve performance are now required by default.
 * variance_stokes_linear() does not default through zero anymore.
+* Refactored calibration_single_ended and calibration_double_ended()
+* Moved ParameterIndices classes to calibration_utils.py
 * Flox included in requirements to speed up resampling via xarray ([Xarray #5734](https://github.com/pydata/xarray/pull/5734)).
 
 Removed
diff --git a/src/dtscalibration/datastore.py b/src/dtscalibration/datastore.py
index 3323c414..1c32e781 100644
--- a/src/dtscalibration/datastore.py
+++ b/src/dtscalibration/datastore.py
@@ -13,6 +13,8 @@
 from scipy.optimize import minimize
 from scipy.sparse import linalg as ln
 
+from dtscalibration.calibrate_utils import calibration_single_ended_helper
+from dtscalibration.calibrate_utils import calibration_double_ended_helper
 from dtscalibration.calibrate_utils import match_sections
 from dtscalibration.calibrate_utils import parse_st_var
 from dtscalibration.datastore_utils import ParameterIndexDoubleEnded
@@ -1931,7 +1933,8 @@ def calibration_single_ended(
         )
 
         if method == "wls":
-            p_cov, p_val, p_var = self.calibration_single_ended_helper(
+            p_cov, p_val, p_var = calibration_single_ended_helper(
+                self,
                 st_var,
                 ast_var,
                 fix_alpha,
@@ -2382,7 +2385,8 @@ def calibration_double_ended(
             matching_indices = match_sections(self, matching_sections)
 
         if method == "wls":
-            p_cov, p_val, p_var = self.calibration_double_ended_helper(
+            p_cov, p_val, p_var = calibration_double_ended_helper(
+                self
                 st_var,
                 ast_var,
                 rst_var,