diff --git a/gtsam/navigation/ImuBias.h b/gtsam/navigation/ImuBias.h
index d52b4eb298..fad952232f 100644
--- a/gtsam/navigation/ImuBias.h
+++ b/gtsam/navigation/ImuBias.h
@@ -29,8 +29,8 @@ namespace imuBias {
 
 class GTSAM_EXPORT ConstantBias {
 private:
-  Vector3 biasAcc_;
-  Vector3 biasGyro_;
+  Vector3 biasAcc_; ///< The units for stddev are σ = m/s² or m √Hz/s²
+  Vector3 biasGyro_; ///< The units for stddev are σ = rad/s or rad √Hz/s
 
 public:
   /// dimension of the variable - used to autodetect sizes
diff --git a/gtsam/navigation/PreintegratedRotation.h b/gtsam/navigation/PreintegratedRotation.h
index 0e0559a32d..e52d28e1ef 100644
--- a/gtsam/navigation/PreintegratedRotation.h
+++ b/gtsam/navigation/PreintegratedRotation.h
@@ -29,7 +29,9 @@ namespace gtsam {
 /// Parameters for pre-integration:
 /// Usage: Create just a single Params and pass a shared pointer to the constructor
 struct GTSAM_EXPORT PreintegratedRotationParams {
-  Matrix3 gyroscopeCovariance;  ///< continuous-time "Covariance" of gyroscope measurements
+  /// Continuous-time "Covariance" of gyroscope measurements
+  /// The units for stddev are σ = rad/s/√Hz
+  Matrix3 gyroscopeCovariance;
   boost::optional<Vector3> omegaCoriolis;  ///< Coriolis constant
   boost::optional<Pose3> body_P_sensor;    ///< The pose of the sensor in the body frame
 
diff --git a/gtsam/navigation/PreintegrationParams.h b/gtsam/navigation/PreintegrationParams.h
index ce1f0e7346..960f67e249 100644
--- a/gtsam/navigation/PreintegrationParams.h
+++ b/gtsam/navigation/PreintegrationParams.h
@@ -24,7 +24,9 @@ namespace gtsam {
 /// Parameters for pre-integration:
 /// Usage: Create just a single Params and pass a shared pointer to the constructor
 struct GTSAM_EXPORT PreintegrationParams: PreintegratedRotationParams {
-  Matrix3 accelerometerCovariance; ///< continuous-time "Covariance" of accelerometer
+  /// Continuous-time "Covariance" of accelerometer
+  /// The units for stddev are σ = m/s²/√Hz
+  Matrix3 accelerometerCovariance;
   Matrix3 integrationCovariance; ///< continuous-time "Covariance" describing integration uncertainty
   bool use2ndOrderCoriolis; ///< Whether to use second order Coriolis integration
   Vector3 n_gravity; ///< Gravity vector in nav frame