Compass mounted at 90 degrees

I have my compass mounted at 90 degrees to straight ahead with the arrow pointing left. See photo.

In Mission Planner do I set the Yaw correction at 90 or 270 degrees? (I guess it’s yaw correction)

Is the external compass the compass 1 or 2 in the compass setup in Mission Planner on a Pixhawk?

Rotation goes clockwise from the top so use 270 degrees. The external compass is #1. It has the pull-down menu to set rotation.