function seller_roi_calc(form) {
	var time_cost = parseFloat(form.time.value);
	var cost = parseFloat(form.cost.value);
	var profit = parseFloat(form.ord.value);
	
	time_cost = (time_cost / 60.0) * cost;
	//50% comission
	profit = (profit * 0.5) - time_cost;
	form.roi.value = ((profit / time_cost) * 100).toFixed(2);
	
	return true;		
}