function cal(fl1,fl2,fl3) {
	var f1 = document.getElementById(fl1);
	var f2 = document.getElementById(fl2);
	var f3 = document.getElementById(fl3);
	var id = parseFloat(f1.value);
	var tk = parseFloat(f2.value);
	f3.value = parseFloat((id + tk) * 3.1416);
	if(!f3.value || f3.value == "NaN") alert("Please input a number");
}

function cal2(fl1,fl2,fl3,fl4) {
	var f1 = document.getElementById(fl1);
	var f2 = document.getElementById(fl2);
	var f3 = document.getElementById(fl3);
	var f4 = document.getElementById(fl4);

	var weigh = parseFloat(f1.value);
	var knownDesity = parseFloat(f2.value);
	var wantedDesity = parseFloat(f3.value);
	f4.value = weigh / knownDesity * wantedDesity;
	if(f4.value == "NaN") alert("Please input a number");
}

function cal3(fl1,fl2,fl3,fl4,fl5) {
	var f1 = document.getElementById(fl1);
	var f2 = document.getElementById(fl2);
	var f3 = document.getElementById(fl3);
	var f4 = document.getElementById(fl4);
	var f5 = document.getElementById(fl5);

	var length = parseFloat(f1.value);
	var weight = parseFloat(f2.value);
	var thickness = parseFloat(f3.value);
	var desity = parseFloat(f4.value);
	f5.value = length * weight * thickness * desity / 1000;
	if(f5.value == "NaN") alert("Please input a number");
}

function set(obj,hdn) {
	var box = document.getElementById(obj);
	var box2= document.getElementById(hdn);
	box2.value = box.options[box.selectedIndex].value;
}