diff --git a/arduino/sketchDistanceSerial-Ultrasonic.ino b/arduino/sketchDistanceSerial-Ultrasonic.ino
index d29c9d6..fb64cb1 100644
--- a/arduino/sketchDistanceSerial-Ultrasonic.ino
+++ b/arduino/sketchDistanceSerial-Ultrasonic.ino
@@ -1,3 +1,7 @@
+// Ultrasonic - Library for HR-SC04 Ultrasonic Ranging Module.
+// Rev.4 (06/2012) - J.Rodrigo ( www.jrodrigo.net ) - www.ardublog.com
+// more info at https://www.abonnel.fr/electronique/lois-et-composants/500-capteur-de-distance-ultrasons#principe
+
 #include "Ultrasonic.h"
 
 #define echoPin 9 // attach pin D2 Arduino to pin Echo of HC-SR04