A moral barometer is a trusted person who will advise or act in such a way as to protect and guide someone or something.
Paul had a decision to make about his relationship with Jenny. So he turned to his moral barometer Jack for advice and guidance.
Sharon had met with a dodgy
salesman who was pushing her into making a decision. She contacted her moral barometer Frank who gave her the advice and encouragement she needed to manage the situation in her favour.