diff --git a/doc/pprz_algebra/quaternion.tex b/doc/pprz_algebra/quaternion.tex
index 3f3710a9f1..7977222283 100644
--- a/doc/pprz_algebra/quaternion.tex
+++ b/doc/pprz_algebra/quaternion.tex
@@ -27,8 +27,8 @@ Sets a quaternion to the identity rotation (no rotation).
 \inHfile{FLOAT\_QUAT\_ZERO(q)}{pprz\_algebra\_float}
 
 \subsubsection*{$\quat{} = \transp{(\quat i,\quat x,\quat y,\quat z)}$}
-\begin{equation}
 \textit{i} is the real part of the quaternion.
+\begin{equation}
  \quat a = \begin{pmatrix}i\\ x \\ y \\ z \end{pmatrix}
 \end{equation}
 \inHfile{QUAT\_ASSIGN(q, i, x, y, z)}{pprz\_algebra}
@@ -212,4 +212,4 @@ leading to
 \end{pmatrix}
 \multiplication \quat{}
 \end{equation}
-\inHfile{FLOAT\_QUAT\_DERIVATIVE\_LAGRANGE(qd, r, q)}{pprz\_algebra\_float}
\ No newline at end of file
+\inHfile{FLOAT\_QUAT\_DERIVATIVE\_LAGRANGE(qd, r, q)}{pprz\_algebra\_float}
diff --git a/sw/airborne/fms/libeknav/test_libeknav_4.cpp b/sw/airborne/fms/libeknav/test_libeknav_4.cpp
index 94cc35623a..f5ac55b230 100644
--- a/sw/airborne/fms/libeknav/test_libeknav_4.cpp
+++ b/sw/airborne/fms/libeknav/test_libeknav_4.cpp
@@ -3,7 +3,6 @@
 
 #include <stdlib.h>
 
- 
 struct timespec start, prev;
 FILE* ins_logfile;		// note: initilaized in init_ins_state
 unsigned int counter;
@@ -142,16 +141,28 @@ static void main_run_ins(uint8_t data_valid) {
   clock_gettime(TIMER, &now);
   
   double dt_imu_freq = 0.001953125; //  1/512; // doesn't work?
-  
+  #if SYNTHETIC_MAG_MODE
+  ins.predict(Vector3d::Zero(), Vector3d(0,0,-GRAVITY), dt_imu_freq);
+  #else
   ins.predict(RATES_AS_VECTOR3D(imu_float.gyro), VECT3_AS_VECTOR3D(imu_float.accel), dt_imu_freq);
+  #endif
   
   if(MAG_READY(data_valid)){
+		#if SYNTHETIC_MAG_MODE
+		DoubleVect3 ref_dir_ned;
+		EARTHS_GEOMAGNETIC_FIELD_NORMED(ref_dir_ned);
+		std::cout << "MAG-UPDATE\t";
+		ins.obs_vector(reference_direction, VECT3_AS_VECTOR3D(ref_dir_ned), mag_noise);
+		//ins.obs_vector(reference_direction, reference_direction, mag_noise);
+		#else
 		ins.obs_vector(reference_direction, VECT3_AS_VECTOR3D(imu_float.mag), mag_noise);
+		#endif
 	}
   
   #if UPDATE_WITH_GRAVITY
   if(CLOSE_TO_GRAVITY(imu_float.accel)){
 		// use the gravity as reference
+		std::cout << "GRAV-UPDATE\t";
 		ins.obs_vector(ins.avg_state.position.normalized(), VECT3_AS_VECTOR3D(imu_float.accel), 1.0392e-3);
 	}
   #endif
@@ -162,7 +173,6 @@ static void main_run_ins(uint8_t data_valid) {
   
   print_estimator_state(absTime(time_diff(now, start)));
   
-  
 }
 #endif
 
@@ -196,6 +206,11 @@ static void init_ins_state(void){
 	LLA_ASSIGN(pos_0_lla, TOULOUSE_LATTITUDE, TOULOUSE_LONGITUDE, TOULOUSE_HEIGHT)
 	PPRZ_LLA_TO_EIGEN_ECEF(pos_0_lla, pos_0_ecef);
 	
+	#if SYNTHETIC_MAG_MODE
+	//pos_0_ecef = Vector3d(4627511.37,119627.69,4373302.43);			// measured at ??
+	pos_0_ecef = Vector3d(4625562,115469,4375209);			
+	#endif
+	
 	printf("Starting position\t%f\t%f\t%f\n", pos_0_ecef(0), pos_0_ecef(1), pos_0_ecef(2));
 	
 	ins.avg_state.position    = pos_0_ecef;
diff --git a/sw/airborne/fms/libeknav/test_libeknav_4.hpp b/sw/airborne/fms/libeknav/test_libeknav_4.hpp
index f4ad3d4dc0..d2ed66bc80 100644
--- a/sw/airborne/fms/libeknav/test_libeknav_4.hpp
+++ b/sw/airborne/fms/libeknav/test_libeknav_4.hpp
@@ -37,7 +37,7 @@ extern "C" {
 /* constants */
 /** Compilation-control **/
 #define RUN_FILTER 1
-#define UPDATE_WITH_GRAVITY 0
+#define UPDATE_WITH_GRAVITY 1
 #define SYNTHETIC_MAG_MODE 1
 #define FILTER_OUTPUT_IN_NED 1