function onlynumber(myfield, e,tolerado)
{
	if (myfield.length ==0)
		myfield.value=0;  
	
	var key;
	var keychar;
	
	if (window.event)
		key = window.event.keyCode;
	else if (e)
		key = e.which;
	else
		return true;
	
	keychar = String.fromCharCode(key);
	
	if ((key==null) || (key==0) || (key==8) || (key==9)|| (key==13)|| (key==27) )
		return true;
	else if ((("0123456789"+tolerado).indexOf(keychar) > -1)){
		if (((myfield.value).indexOf(tolerado) > -1)&&(keychar==tolerado))
			return false;
		else if ((myfield.value.length==0)&&(keychar==tolerado))
		{
			myfield.value = "0";
			return true;	
		}
		else
			return true;
	}
	else
		return false;	
}