diff --git a/app/src/main/java/com/google/android/stardroid/activities/DynamicStarMapActivity.java b/app/src/main/java/com/google/android/stardroid/activities/DynamicStarMapActivity.java
index 1ec11e328..93b30134b 100644
--- a/app/src/main/java/com/google/android/stardroid/activities/DynamicStarMapActivity.java
+++ b/app/src/main/java/com/google/android/stardroid/activities/DynamicStarMapActivity.java
@@ -127,8 +127,8 @@ public void run() {
 
       rendererController.queueSetViewOrientation(directionX, directionY, directionZ, upX, upY, upZ);
 
-      Vector3 acceleration = model.getPhoneAcceleration();
-      rendererController.queueTextAngle(MathUtil.atan2(-acceleration.x, -acceleration.y));
+      Vector3 up = model.getPhoneUpDirection();
+      rendererController.queueTextAngle(MathUtil.atan2(up.x, up.y));
       rendererController.queueViewerUpDirection(model.getZenith().copy());
 
       float fieldOfView = model.getFieldOfView();
@@ -563,8 +563,7 @@ public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, Strin
         setAutoMode(autoMode);
         break;
       case ApplicationConstants.SHARED_PREFERENCE_EXPERIMENTAL_USE_GYRO:
-        boolean useGyro = sharedPreferences.getBoolean(key, false);
-        model.setUseRotationVector(useGyro);
+        // Do nothing - the sensor controller will take care of it.
       default:
         return;
     }
diff --git a/app/src/main/java/com/google/android/stardroid/control/AstronomerModel.java b/app/src/main/java/com/google/android/stardroid/control/AstronomerModel.java
index 4cf52023f..56ad630b6 100644
--- a/app/src/main/java/com/google/android/stardroid/control/AstronomerModel.java
+++ b/app/src/main/java/com/google/android/stardroid/control/AstronomerModel.java
@@ -28,10 +28,6 @@
  * @author John Taylor
  */
 public interface AstronomerModel {
-
-
-  void setUseRotationVector(boolean useRotationVector);
-
   /**
    * A POJO to hold the user's view direction.
    *
@@ -156,7 +152,7 @@ void updateLineOfSight(Vector3 newLineOfSight) {
    * 
    * <p>The returned object should not be modified.
    */
-  Vector3 getPhoneAcceleration();
+  Vector3 getPhoneUpDirection();
 
   /**
    * Sets the acceleration and magnetic field in the phone frame.
diff --git a/app/src/main/java/com/google/android/stardroid/control/AstronomerModelImpl.java b/app/src/main/java/com/google/android/stardroid/control/AstronomerModelImpl.java
index 4825a6ba3..500ac6737 100644
--- a/app/src/main/java/com/google/android/stardroid/control/AstronomerModelImpl.java
+++ b/app/src/main/java/com/google/android/stardroid/control/AstronomerModelImpl.java
@@ -96,6 +96,8 @@ public class AstronomerModelImpl implements AstronomerModel {
   /** The sensor acceleration in the phone's coordinate system. */
   private Vector3 acceleration = ApplicationConstants.INITIAL_DOWN.copy();
 
+  private Vector3 upPhone = Geometry.scaleVector(acceleration, -1);
+
   /** The sensor magnetic field in the phone's coordinate system. */
   private Vector3 magneticField = ApplicationConstants.INITIAL_SOUTH.copy();
 
@@ -163,8 +165,8 @@ public void setLocation(LatLong location) {
   }
 
   @Override
-  public Vector3 getPhoneAcceleration() {
-    return acceleration;
+  public Vector3 getPhoneUpDirection() {
+    return upPhone;
   }
 
   private static final float TOL = 0.01f;
@@ -303,7 +305,6 @@ private void calculateLocalNorthAndUpInCelestialCoords(boolean forceUpdate) {
    */
   private void calculateLocalNorthAndUpInPhoneCoordsFromSensors() {
     Vector3 magneticNorthPhone;
-    Vector3 upPhone;
     Vector3 magneticEastPhone;
     if (useRotationVector) {
       float[] rotationMatrix = new float[9];
@@ -327,7 +328,6 @@ private void calculateLocalNorthAndUpInPhoneCoordsFromSensors() {
       upPhone = scaleVector(down, -1);
       magneticEastPhone = vectorProduct(magneticNorthPhone, upPhone);
     }
-
     // The matrix is orthogonal, so transpose it to find its inverse.
     // Easiest way to do that is to construct it from row vectors instead
     // of column vectors.
@@ -367,9 +367,4 @@ public void setClock(Clock clock) {
   public long getTimeMillis() {
     return clock.getTimeInMillisSinceEpoch();
   }
-
-  @Override
-  public void setUseRotationVector(boolean useRotationVector) {
-    this.useRotationVector = useRotationVector;
-  }
 }
diff --git a/app/src/main/java/com/google/android/stardroid/util/Geometry.java b/app/src/main/java/com/google/android/stardroid/util/Geometry.java
index 923b7c655..28ac56c7a 100644
--- a/app/src/main/java/com/google/android/stardroid/util/Geometry.java
+++ b/app/src/main/java/com/google/android/stardroid/util/Geometry.java
@@ -14,14 +14,14 @@
 
 package com.google.android.stardroid.util;
 
-import java.util.Date;
-
 import com.google.android.stardroid.units.GeocentricCoordinates;
 import com.google.android.stardroid.units.LatLong;
 import com.google.android.stardroid.units.Matrix33;
 import com.google.android.stardroid.units.RaDec;
 import com.google.android.stardroid.units.Vector3;
 
+import java.util.Date;
+
 /**
  * Utilities for working with angles, distances, matrices, and time.
  *
@@ -77,7 +77,7 @@ public static Vector3 vectorProduct(Vector3 v1, Vector3 v2) {
   }
 
   /**
-   * Scales the vector by the given amount
+   * Scales the vector by the given amount and returns a new vector.
    */
   public static Vector3 scaleVector(Vector3 v, float scale) {
     return new Vector3 (scale * v.x, scale * v.y, scale * v.z);