diff --git a/owlps-positioner/src/autocalibration.cc b/owlps-positioner/src/autocalibration.cc
index 3f1427d..e3a3b78 100644
--- a/owlps-positioner/src/autocalibration.cc
+++ b/owlps-positioner/src/autocalibration.cc
@@ -86,6 +86,13 @@ void Autocalibration::generate_ss()
   if (rx_coord.get_z() != point.get_z())
     return ;
 
+  /* Compute the origin angle P-RX-O */
+  Point3D origin(rx_coord) ;
+  origin.set_x(rx_coord.get_x() + 10) ;
+  origin_angle = rx_coord.angle_2d(point, origin) ;
+  if (point.get_y() > rx_coord.get_y())
+    origin_angle = -origin_angle ;
+
   /* Choose the nearest AP(s) in angle */
   sort_reference_aps() ;
   // We need at least one reference AP:
@@ -146,7 +153,7 @@ void Autocalibration::sort_reference_aps()
 
       /* Rotate the AP's coordinates to know the angle direction */
       Point3D ref_coord_r(ref_coord) ;
-      ref_coord_r.rotate_2d(rx_coord, angle_p) ;
+      ref_coord_r.rotate_2d(rx_coord, origin_angle) ;
       // Insert the AP in the right list, according to the direction:
       if (ref_coord_r.get_y() < rx_coord.get_y())
         sorted_negative_angles.insert(weight_angle_ap) ;
diff --git a/owlps-positioner/src/autocalibration.hh b/owlps-positioner/src/autocalibration.hh
index 7b9347d..2072f3b 100644
--- a/owlps-positioner/src/autocalibration.hh
+++ b/owlps-positioner/src/autocalibration.hh
@@ -32,7 +32,7 @@ private:
   /// Current AP to generate a SS for
   std::tr1::unordered_map<std::string, AccessPoint>::const_iterator rx ;
   /// Angle P-RX-O, O being the origin of the trigonometric circle
-  float angle_p ;
+  float origin_angle ;
   /// Selected transmitter APs
   std::vector<ap> ref_aps ;
   /// \brief Angles of the transmitter APs (before M on the trigonometric