diff --git a/ArduCopter/Attitude.cpp b/ArduCopter/Attitude.cpp
index c579e97ccf..893e449db2 100644
--- a/ArduCopter/Attitude.cpp
+++ b/ArduCopter/Attitude.cpp
@@ -170,6 +170,8 @@ float Copter::get_surface_tracking_climb_rate(int16_t target_rate, float current
 
     uint32_t now = millis();
 
+    target_rangefinder_alt_used = true;
+
     // reset target altitude if this controller has just been engaged
     if (now - last_call_ms > RANGEFINDER_TIMEOUT_MS) {
         target_rangefinder_alt = rangefinder_state.alt_cm + current_alt_target - current_alt;
diff --git a/ArduCopter/Copter.h b/ArduCopter/Copter.h
index f7160a885e..18b1c18e0e 100644
--- a/ArduCopter/Copter.h
+++ b/ArduCopter/Copter.h
@@ -463,6 +463,7 @@ private:
     // The cm/s we are moving up or down based on filtered data - Positive = UP
     int16_t climb_rate;
     float target_rangefinder_alt;   // desired altitude in cm above the ground
+    bool target_rangefinder_alt_used; // true if mode is using target_rangefinder_alt
     int32_t baro_alt;            // barometer altitude in cm above home
     float baro_climbrate;        // barometer climbrate in cm/s
     LowPassFilterVector3f land_accel_ef_filter; // accelerations for land and crash detector tests
diff --git a/ArduCopter/Log.cpp b/ArduCopter/Log.cpp
index cd0f3d4303..394cac7738 100644
--- a/ArduCopter/Log.cpp
+++ b/ArduCopter/Log.cpp
@@ -102,7 +102,7 @@ struct PACKED log_Control_Tuning {
     float    desired_alt;
     float    inav_alt;
     int32_t  baro_alt;
-    int16_t  desired_rangefinder_alt;
+    float    desired_rangefinder_alt;
     int16_t  rangefinder_alt;
     float    terr_alt;
     int16_t  target_climb_rate;
@@ -120,6 +120,12 @@ void Copter::Log_Write_Control_Tuning()
     }
 #endif
 
+    float _target_rangefinder_alt;
+    if (target_rangefinder_alt_used) {
+        _target_rangefinder_alt = target_rangefinder_alt * 0.01f; // cm->m
+    } else {
+        _target_rangefinder_alt = DataFlash.quiet_nan();
+    }
     struct log_Control_Tuning pkt = {
         LOG_PACKET_HEADER_INIT(LOG_CONTROL_TUNING_MSG),
         time_us             : AP_HAL::micros64(),
@@ -130,7 +136,7 @@ void Copter::Log_Write_Control_Tuning()
         desired_alt         : pos_control->get_alt_target() / 100.0f,
         inav_alt            : inertial_nav.get_altitude() / 100.0f,
         baro_alt            : baro_alt,
-        desired_rangefinder_alt : (int16_t)target_rangefinder_alt,
+        desired_rangefinder_alt : _target_rangefinder_alt,
         rangefinder_alt     : rangefinder_state.alt_cm,
         terr_alt            : terr_alt,
         target_climb_rate   : (int16_t)pos_control->get_vel_target_z(),
@@ -492,7 +498,7 @@ const struct LogStructure Copter::log_structure[] = {
       "OF",   "QBffff",   "TimeUS,Qual,flowX,flowY,bodyX,bodyY", "s-EEEE", "F-0000" },
 #endif
     { LOG_CONTROL_TUNING_MSG, sizeof(log_Control_Tuning),
-      "CTUN", "Qffffffeccfhh", "TimeUS,ThI,ABst,ThO,ThH,DAlt,Alt,BAlt,DSAlt,SAlt,TAlt,DCRt,CRt", "s----mmmmmmnn", "F----00BBBBBB" },
+      "CTUN", "Qffffffefcfhh", "TimeUS,ThI,ABst,ThO,ThH,DAlt,Alt,BAlt,DSAlt,SAlt,TAlt,DCRt,CRt", "s----mmmmmmnn", "F----00B0BBBB" },
     { LOG_MOTBATT_MSG, sizeof(log_MotBatt),
       "MOTB", "Qffff",  "TimeUS,LiftMax,BatVolt,BatRes,ThLimit", "s-vw-", "F-00-" },
     { LOG_EVENT_MSG, sizeof(log_Event),         
diff --git a/ArduCopter/mode.cpp b/ArduCopter/mode.cpp
index a9ca196e3c..b7a3010f3a 100644
--- a/ArduCopter/mode.cpp
+++ b/ArduCopter/mode.cpp
@@ -247,6 +247,8 @@ void Copter::update_flight_mode()
     // Update EKF speed limit - used to limit speed when we are using optical flow
     ahrs.getEkfControlLimits(ekfGndSpdLimit, ekfNavVelGainScaler);
 
+    target_rangefinder_alt_used = false;
+
     flightmode->run();
 }