Mounting external compass facing/arrow rearward


I want to mount my external compass facing rearward (see picture). How to compensate orientation correctly ? What is the best way to parametrize this ?
I don’t found any correct COMPASS_ORIENTATION for that. If I use Declination 180 degree it seems to be ok but I can’t use Autodeclinasion with that…

This is my actual parameter, but it’s bad because I can’t use COMPASS_AUTODEC.

Can you help me please?

APM:2.6 - FW:3.2 - QuadriCopter

(full size

Thanks !

Set COMPASS_ORIENT to 4 for Yaw 180.

I had tried this, but look the compass behaviour with this value:

How does the compass respond when set up facing forward’s as it expects?

Perfectly when facing forward with COMPASS_ORIENTATION=8