$('#WEcombo_primer select').change(
function(){
calculate_quantity();
}
);

$('.Chosen_Fields input').keyup(
function(){
calculate_quantity();
}
);

function calculate_quantity(){
var $area = $('#WEedit_primer_width input').val() * $('#WEedit_primer_height input').val();
if (($area>0)&&($('#WEcombo_primer select').val()>0)){
$('#WEedit_primer_qty_calc input').val(Math.ceil($area / $('#WEcombo_primer select').val()));
} else {
$('#WEedit_primer_qty_calc input').val("");
}
}

// Action calculation on drop list change
$('#WEcombo_primer select').change(
function(){
calculate_quantity();
}
);

// Action calculation after each key up in selected input fields
$('.Chosen_Fields input').keyup(
function(){
calculate_quantity();
}
);

// update calculated field
function calculate_quantity(){
var $area = 0;
// if drop list selection is ok
if($('#WEcombo_primer select').val()=="Bonding Plaster Primer"){
$area = $('#WEedit_primer_width input').val() * $('#WEedit_primer_height input').val();
if ($area>0){
$('#WEedit_primer_qty_calc input').val(Math.ceil($area / 3.6));
}
} else {
$('#WEedit_primer_qty_calc input').val("");
}
}