I am a Ph.D. student in a country where everyone is addressed by their first name (professors etc.). I call my advisors by their first names and when we have visitors in our research group I go by this rule. However, now I am visiting a German university and I don't really know how to address the professor who has invited me. Before my stay, I would call him by his first name - but now that I have met him at his university and his Ph.D. students (who seem to call him Prof. X) I am becoming unsure about it. Consequently, I have been very inconsistent with how I have been addressing him.
My questions are:
- should I apologize for being inconsistent/possibly being rude? Or am I overthinking this?
- how should I address him?