Stoker/wife has a Myrrycle bar end mirror. Her responsibility is what is behind us and approaching, and navigation (she has the Garmin - I use a Flight Deck). I'm focused on what's ahead and gearing. I'll ask for clear if I need to move over for a left turn, or she will ask if she needs to call "car back" on lightly traveled back roads, and for calling out turns. If she trust me for safely captaining the route, I'll trust her for the safety of approaching traffic and navigation.