<script>
function GetDays(){
var dropdt = new Date(document.getElementById("drop_date").value);
var pickdt = new Date(document.getElementById("pick_date").value);
return parseInt((dropdt - pickdt) / (24 * 3600 * 1000));
}
function cal(){
if(document.getElementById("drop_date")){
document.getElementById("numdays2").value=GetDays( );
}
}
</script>