There is a magnetic heading sensor built into the design. It’s used now to speed up the initial satellite heading calculations at startup, but Furuno plans to “deliver a software upgrade that will provide full magnetic automatic backup in the case of 100% GNSS blockage!” The company was hesitant to advertise this feature before it met their “stringent QC tests” but they’re “confident” about that now. So any update on this as I would like to unplug my flux gate as back up.