diff --git a/src/drivers/px4fmu/fmu.cpp b/src/drivers/px4fmu/fmu.cpp
index e547245367..761a23c426 100644
--- a/src/drivers/px4fmu/fmu.cpp
+++ b/src/drivers/px4fmu/fmu.cpp
@@ -505,7 +505,11 @@ PX4FMU::task_main()
 			orb_copy(ORB_ID(actuator_armed), _t_armed, &aa);
 
 			/* update PWM servo armed status if armed and not locked down */
-			up_pwm_servo_arm(aa.armed && !aa.lockdown);
+			bool set_armed = aa.armed && !aa.lockdown;
+			if (set_armed != _armed) {
+				_armed = set_armed;
+				up_pwm_servo_arm(set_armed);
+			}
 		}
 
 		// see if we have new PPM input data
diff --git a/src/modules/commander/accelerometer_calibration.c b/src/modules/commander/accelerometer_calibration.c
index 991145d73c..d79dd93dd0 100644
--- a/src/modules/commander/accelerometer_calibration.c
+++ b/src/modules/commander/accelerometer_calibration.c
@@ -232,7 +232,6 @@ int detect_orientation(int mavlink_fd, int sub_sensor_combined) {
 	float accel_ema[3] = { 0.0f, 0.0f, 0.0f };
 	/* max-hold dispersion of accel */
 	float accel_disp[3] = { 0.0f, 0.0f, 0.0f };
-	float accel_len2 = 0.0f;
 	/* EMA time constant in seconds*/
 	float ema_len = 0.2f;
 	/* set "still" threshold to 0.1 m/s^2 */
@@ -304,30 +303,29 @@ int detect_orientation(int mavlink_fd, int sub_sensor_combined) {
 		}
 	}
 
-	float accel_len = sqrt(accel_len2);
-	if (  fabs(accel_ema[0] - accel_len) < accel_err_thr &&
+	if (  fabs(accel_ema[0] - CONSTANTS_ONE_G) < accel_err_thr &&
 		  fabs(accel_ema[1]) < accel_err_thr &&
 		  fabs(accel_ema[2]) < accel_err_thr  )
 		return 0;	// [ g, 0, 0 ]
-	if (  fabs(accel_ema[0] + accel_len) < accel_err_thr &&
+	if (  fabs(accel_ema[0] + CONSTANTS_ONE_G) < accel_err_thr &&
 		  fabs(accel_ema[1]) < accel_err_thr &&
 		  fabs(accel_ema[2]) < accel_err_thr  )
 		return 1;	// [ -g, 0, 0 ]
 	if (  fabs(accel_ema[0]) < accel_err_thr &&
-		  fabs(accel_ema[1] - accel_len) < accel_err_thr &&
+		  fabs(accel_ema[1] - CONSTANTS_ONE_G) < accel_err_thr &&
 		  fabs(accel_ema[2]) < accel_err_thr  )
 		return 2;	// [ 0, g, 0 ]
 	if (  fabs(accel_ema[0]) < accel_err_thr &&
-		  fabs(accel_ema[1] + accel_len) < accel_err_thr &&
+		  fabs(accel_ema[1] + CONSTANTS_ONE_G) < accel_err_thr &&
 		  fabs(accel_ema[2]) < accel_err_thr  )
 		return 3;	// [ 0, -g, 0 ]
 	if (  fabs(accel_ema[0]) < accel_err_thr &&
 		  fabs(accel_ema[1]) < accel_err_thr &&
-		  fabs(accel_ema[2] - accel_len) < accel_err_thr  )
+		  fabs(accel_ema[2] - CONSTANTS_ONE_G) < accel_err_thr  )
 		return 4;	// [ 0, 0, g ]
 	if (  fabs(accel_ema[0]) < accel_err_thr &&
 		  fabs(accel_ema[1]) < accel_err_thr &&
-		  fabs(accel_ema[2] + accel_len) < accel_err_thr  )
+		  fabs(accel_ema[2] + CONSTANTS_ONE_G) < accel_err_thr  )
 		return 5;	// [ 0, 0, -g ]
 
 	mavlink_log_info(mavlink_fd, "ERROR: invalid orientation");
diff --git a/src/modules/commander/accelerometer_calibration.h b/src/modules/commander/accelerometer_calibration.h
index c0169c2a13..a11cf93d3c 100644
--- a/src/modules/commander/accelerometer_calibration.h
+++ b/src/modules/commander/accelerometer_calibration.h
@@ -1,8 +1,8 @@
 /*
  * accelerometer_calibration.h
  *
- *  Created on: 25.04.2013
- *      Author: ton
+ *   Copyright (C) 2013 Anton Babushkin. All rights reserved.
+ *   Author: 	Anton Babushkin	<rk3dov@gmail.com>
  */
 
 #ifndef ACCELEROMETER_CALIBRATION_H_