Better exception for get_acquisition_values

handel/interface.py

@@ -589,7 +589,8 @@ def get_acquisition_value(name, channel=None):
         # Inconsistency
         if value is None:
             raise ValueError(
-                'The acquisition value differs from channel to channel')
+                'The acquisition value {} differs from channel to channel'
+                .format(name))
         # Return
         return value
     # Get value for a single channel