function calculate() {
	var f = document.getElementById("F<sub>1</sub>").value;
	var x = document.getElementById("x").value;
	var moment = "";
	if (f != "" && x != "") {
		f = parseFloat(f);
		x = parseFloat(x);
		moment = f * x;
		document.getElementById("Moment").innerHTML = "moment: " + moment;
	}
}