diff --git a/libraries/AP_Arming/AP_Arming.cpp b/libraries/AP_Arming/AP_Arming.cpp
index 2a3ac5e11b..3a8d3e7e2b 100644
--- a/libraries/AP_Arming/AP_Arming.cpp
+++ b/libraries/AP_Arming/AP_Arming.cpp
@@ -21,6 +21,7 @@
 // this can also be overridden for specific boards in the HAL
 #define AP_ARMING_COMPASS_OFFSETS_MAX   600
 #endif
+#define AP_ARMING_COMPASS_MAGFIELD_EXPECTED 530
 #define AP_ARMING_COMPASS_MAGFIELD_MIN  185     // 0.35 * 530 milligauss
 #define AP_ARMING_COMPASS_MAGFIELD_MAX  875     // 1.65 * 530 milligauss
 #define AP_ARMING_BOARD_VOLTAGE_MIN     4.3f
@@ -88,6 +89,11 @@ AP_Arming::AP_Arming(const AP_AHRS &ahrs_ref, const AP_Baro &baro, Compass &comp
     memset(last_gyro_pass_ms, 0, sizeof(last_gyro_pass_ms));
 }
 
+uint16_t AP_Arming::compass_magfield_expected() const
+{
+    return AP_ARMING_COMPASS_MAGFIELD_EXPECTED;
+}
+
 bool AP_Arming::is_armed()
 { 
     return require == NONE || armed; 
diff --git a/libraries/AP_Arming/AP_Arming.h b/libraries/AP_Arming/AP_Arming.h
index 9271370cec..1820be8e3c 100644
--- a/libraries/AP_Arming/AP_Arming.h
+++ b/libraries/AP_Arming/AP_Arming.h
@@ -65,6 +65,8 @@ public:
 
     static const struct AP_Param::GroupInfo        var_info[];
 
+    uint16_t compass_magfield_expected() const;
+
 protected:
     // Parameters
     AP_Int8                 require;
@@ -96,7 +98,7 @@ protected:
 
     virtual bool ins_checks(bool report);
 
-    bool compass_checks(bool report);
+    virtual bool compass_checks(bool report);
 
     bool gps_checks(bool report);
 
@@ -109,4 +111,5 @@ protected:
     bool manual_transmitter_checks(bool report);
 
     virtual enum HomeState home_status() const = 0;
+
 };