dataset_validator: update error message

nabu/resources/dataset_validator.py

@@ -58,7 +58,7 @@ class NabuValidator(object):
         ny = nx
         if self.nabu_config["reconstruction"]["enable_halftomo"]:
             if self.dataset_infos.axis_position is None:
-                raise ValueError("rotation_axis_position should be either a number or 'auto' for half tomo")
+                raise ValueError("Cannot use rotation axis position in the middle of the detector when half tomo is enabled")
             cor = int(round(self.dataset_infos.axis_position))
             ny = nx = 2*cor
         what = (