diff --git a/nasco_analysis/io.py b/nasco_analysis/io.py
index 4acc403..f7a697c 100644
--- a/nasco_analysis/io.py
+++ b/nasco_analysis/io.py
@@ -117,7 +117,7 @@ def create_tp_array(self) -> xr.Dataset:
             )
         return self.data_set
 
-    def correct_kisa(self) -> Tuple[np.ndarray]:
+    def correct_kisa(self) -> Tuple[xr.DataArray]:
         if self.kisa_path is None:
             self.encoder_set = self.encoder_set.rename(
                 {"enc_az": "az", "enc_el": "el"}
@@ -139,6 +139,9 @@ def correct_kisa(self) -> Tuple[np.ndarray]:
 
         return az, el
 
+    def correct_collimation_error(self) -> Tuple[xr.DataArray]:
+        return NotImplemented
+
     def combine_metadata(self, int_obsmode: bool = False) -> xr.DataArray:
         self.correct_kisa()