When using a Garmin GTX-345 for AHRS data with ForeFlight Mobile, the AHRS calibration can be fine-tuned from within the app. Pitch and roll values for the GTX-345 must initially be calibrated by your avionics shop during installation.
To calibrate the GTX-345 AHRS in ForeFlight Mobile,
STEP 1. Tap the AHRS SETTINGS button in the attitude display (gear icon), above the fullscreen button. This will activate Zero Pitch & Bank mode and a blue SAVE button will appear in the upper left corner of the display.
STEP 2. Adjust your aircraft so that it is straight and level, then tap the ZERO PITCH & BANK button to zero the display.
STEP 3. Tap the SAVE button to save the AHRS calibration.
Steps to calibrate AHRS