function DateObser() {

if (document.getElementById("nuit").checked) MyHunt=document.getElementById("nuit").value;
if (document.getElementById("passee").checked) MyHunt=document.getElementById("passee").value;
if (document.getElementById("volee").checked) MyHunt=document.getElementById("volee").value;
if (document.getElementById("journee").checked) MyHunt=document.getElementById("journee").value;

MyDate = new Date(document.getElementsByName("Date_y")[0].value,document.getElementsByName("Date_m")[0].value-1,document.getElementsByName("Date_d")[0].value) 
MyDate2=new Date(MyDate);
NewTime=MyDate2.getTime()-86400000;
MyDate2.setTime(NewTime);
	switch(MyHunt) {
		case "1":
		Msg="Nuit du "+MyDate2.getDate()+" au "+MyDate.getDate()+"/"+(MyDate.getMonth()+1)+"/"+MyDate.getFullYear();
 		break;
		case "3":
			Msg="Volée du "+MyDate.getDate()+"/"+(MyDate.getMonth()+1)+"/"+MyDate.getFullYear();
 		break;
		case "2":
			Msg="Passée du "+MyDate.getDate()+"/"+(MyDate.getMonth()+1)+"/"+MyDate.getFullYear();
 		break;
		case "4":
			Msg="Le "+MyDate.getDate()+"/"+(MyDate.getMonth()+1)+"/"+MyDate.getFullYear();
 		break;
	}
  document.getElementById("DateAff").innerHTML=Msg;
	document.getElementById("DateHidden").value=Msg;
}