diff --git a/gtsam_unstable/slam/Mechanization_bRn2.cpp b/gtsam_unstable/slam/Mechanization_bRn2.cpp
index 312814d15..91cc17f6d 100644
--- a/gtsam_unstable/slam/Mechanization_bRn2.cpp
+++ b/gtsam_unstable/slam/Mechanization_bRn2.cpp
@@ -83,14 +83,21 @@ Mechanization_bRn2 Mechanization_bRn2::integrate(const Vector& u,
     const double dt) const {
   // integrate rotation nRb based on gyro measurement u and bias x_g
 
+#ifndef MODEL_NAV_FRAME_ROTATION
   // get body to inertial (measured in b) from gyro, subtract bias
   Vector b_omega_ib = u - x_g_;
 
-  // assume nav to inertial through movement is unknown
+  // nav to inertial due to Earth's rotation and our movement on Earth surface
+  // TODO: figure out how to do this if we need it
   Vector b_omega_in = zero(3);
 
-  // get angular velocity on bRn measured in body frame
+  // calculate angular velocity on bRn measured in body frame
   Vector b_omega_bn = b_omega_in - b_omega_ib;
+#else
+  // Assume a non-rotating nav frame (probably an approximation)
+  // calculate angular velocity on bRn measured in body frame
+  Vector b_omega_bn = x_g_ - u;
+#endif
 
   // convert to navigation frame
   Rot3 nRb = bRn_.inverse();
diff --git a/gtsam_unstable/slam/tests/testAHRS.cpp b/gtsam_unstable/slam/tests/testAHRS.cpp
index f9731113b..d59098402 100644
--- a/gtsam_unstable/slam/tests/testAHRS.cpp
+++ b/gtsam_unstable/slam/tests/testAHRS.cpp
@@ -5,11 +5,12 @@
  * @author Chris Beall
  */
 
-#include <list>
+#include "../AHRS.h"
 #include <gtsam/geometry/Rot3.h>
 #include <gtsam/base/Vector.h>
-#include "../AHRS.h"
+#include <gtsam/base/Testable.h>
 #include <CppUnitLite/TestHarness.h>
+#include <list>
 
 using namespace std;
 using namespace gtsam;
@@ -67,6 +68,21 @@ TEST (AHRS, constructor) {
   AHRS ahrs = AHRS(stationaryU,stationaryF,g_e);
 }
 
+/* ************************************************************************* */
+// TODO make a testMechanization_bRn2
+TEST (AHRS, Mechanization_integrate) {
+  AHRS ahrs = AHRS(stationaryU,stationaryF,g_e);
+  Mechanization_bRn2 mech;
+  KalmanFilter::State state;
+//  boost::tie(mech,state) = ahrs.initialize(g_e);
+//  Vector u = Vector_(3,0.05,0.0,0.0);
+//  double dt = 2;
+//  Rot3 expected;
+//  Mechanization_bRn2 mech2 = mech.integrate(u,dt);
+//  Rot3 actual = mech2.bRn();
+//  EXPECT(assert_equal(expected, actual));
+}
+
 /* ************************************************************************* */
 /* TODO: currently fails because of problem with ill-conditioned system
 TEST (AHRS, init) {