Add support for a configurable compass declination in a range of -99 to 99 degrees. This allows the displayed compass reading to be configured to take into account the compass declination (difference between the measured magnetic North direction and the actual geographical North direction) that has different values for different locations around the globe. See https://magnetic-declination.com/ for more information. (mikeller)

--- a/Common/Inc/data_central.h	Thu May 11 12:13:03 2023 +0200
+++ b/Common/Inc/data_central.h	Thu May 18 09:49:17 2023 +0200
@@ -28,6 +28,7 @@
 #define DATA_CENTRAL_H
 
 #include <stdint.h>
+#include <stdbool.h>
 
 #include "settings.h"
 #include "stm32f4xx_hal.h"
@@ -502,5 +503,6 @@
 
 uint8_t isLoopMode(uint8_t Mode);
 
+bool isCompassCalibrated(void);
 void setCompassHeading(uint16_t heading);
 #endif // DATA_CENTRAL_H