When using your iPad or iPhone Compass to set the Anchor Heading, it is possible this may disagree with your boat GPS by +/- 16'. This is due to the compass in your device being less accurate than the boat GPS. iPad and iPhone GPS are not of as high a quality as a dedicated boat GPS.
It is unlikely you will ever fully resolve the variance, however, to troubleshoot this as best possible:
1. Ensure Location Services Are On
Go to Settings > Privacy & Security > Location Services
Make sure Location Services is ON
Scroll down and ensure the Anchor Alert App has access set to "While Using the App" or "Always".
2. Enable Precise Location
Tap your navigation app under Location Services
Enable Precise Location for better accuracy
3. Check Compass Calibration
GPS relies on sensors like the compass, which you can calibrate:
Go to Settings > Privacy & Security > Location Services > System Services
Turn on Compass Calibration
Open the Compass app and move the phone in a figure-8 motion until the compass stabilizes
4. Reset Location & Privacy Settings (if needed)
If GPS is still inaccurate:
Go to Settings > General > Transfer or Reset iPhone > Reset
Tap Reset Location & Privacy
This resets all app location settings—you’ll need to re-allow permissions afterward.
5. Ensure Clear View of the Sky
GPS accuracy depends on satellite visibility
Avoid dense buildings, trees, metal structures, or indoors if possible
6. Toggle Airplane Mode
This can force the phone to refresh its GPS and network data:
Turn Airplane Mode ON, wait 10 seconds, then turn it OFF
7. Reboot the Phone
Sometimes a simple restart fixes stuck location services
8. Update iOS
A bug or outdated iOS can affect GPS accuracy:
Go to Settings > General > Software Update