function update_quantity(champ, increase) {
	// javascript refresher!
	//alert(eval("document.commande."+champ+".value"));
	//alert(champ);

	// retrieve the form item we're checking
	var item = eval("document.commande."+champ);

	// get and check value
	var valeur = item.value;
	if (isNaN(valeur)) {
		valeur = 0;
	} else {
		if (increase > 0) {
			valeur++;
		}
		if (increase < 0) {
			valeur--;
		}
	}
	if (valeur < 0) {
		valeur = 0;
	}

	// update value - quantity
	item.value = valeur;

	// update values - subtotal and total
	update_form();	
}

function update_form() {
	var products = new Array();
	products['bch_001_noir'] = 24.95;
	products['bch_001_blanc'] = 24.95;
	products['bch_001_marron'] = 24.95;
	products['bch_002_noir'] = 24.95;
	products['bch_002_blanc'] = 24.95;
	products['bch_002_marron'] = 24.95;
	products['bch_003_noir'] = 24.95;
	products['bch_004_noir'] = 24.95;

	//document.commande.bch_001_noir_sub.value = 
	var item_qty;
	var item_sub;
	var sum = 0;
	for (prod in products) {
		//alert(prod);
		item_qty = eval("document.commande."+prod);
		item_sub = eval("document.commande."+prod+"_sub");
		item_sub.value = eval(item_qty.value * products[prod]).toFixed(2);
		//alert(item_sub.value);
		sum += eval(item_sub.value);
	}
	document.commande.subtotal.value = eval(sum).toFixed(2);

	// grand total
	document.commande.total.value = eval(eval(document.commande.handlingandshipping.value) + eval(document.commande.subtotal.value)).toFixed(2);
}