diff --git a/ArduCopter/sensors.pde b/ArduCopter/sensors.pde
index 38ab52a235..91f7f8ea8c 100644
--- a/ArduCopter/sensors.pde
+++ b/ArduCopter/sensors.pde
@@ -1,12 +1,5 @@
 // -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
 
- #if CONFIG_SONAR == ENABLED
-static void init_sonar(void)
-{
-    sonar.init();
-}
-#endif
-
 static void init_barometer(bool full_calibration)
 {
     gcs_send_text_P(SEVERITY_LOW, PSTR("Calibrating barometer"));
@@ -41,6 +34,13 @@ static void read_barometer(void)
     }
 }
 
+#if CONFIG_SONAR == ENABLED
+static void init_sonar(void)
+{
+   sonar.init();
+}
+#endif
+
 // return sonar altitude in centimeters
 static int16_t read_sonar(void)
 {
@@ -77,6 +77,7 @@ static int16_t read_sonar(void)
 #endif
 }
 
+// initialise compass
 static void init_compass()
 {
     if (!compass.init() || !compass.read()) {
@@ -88,6 +89,7 @@ static void init_compass()
     ahrs.set_compass(&compass);
 }
 
+// initialise optical flow sensor
 static void init_optflow()
 {
 #if OPTFLOW == ENABLED