DP0503 without compass

Hi guys.
If I use only GPS (without compass), do I need to align the arrow on modue along with drone direction or it doesn’t matter? We’ve got many “GPS glitch” and “ground mag anomaly” errors. Searching for the reason…

Please use the magnetometer which is on the DP0503 or an external one.

tried to connect today but got error “compass inconsistent” in mission planner
set primary to Compass1
compass1 is checked as external, with no rotation
compass2 is not checked as external.

using pixhack 2.4.8, autopilot direction is like an arrow on it. drotek module is the same. what may be the reason of inconsistence?

finally, found the error
need to set YAW270 in comass rotation. I wonder why there’s no info in manual about this that compass is not aligned to the arrow on top of M8N module…