function calculate(x){
	var currency, planetype, enginetaxi, dailyarrivals, reducedtime, avgfuelprice, daysinyear, emissionsrate, monetaryvalue, emissionsvalue;
	
	//Establish constants---------------------------------------------------
	
	avgfuelprice = 2.00;
	daysinyear = 365;
	emissionsrate = 21.095;
	currency = x;
	
	planetype = document.getElementById('plane').value;
	
	//alert("Plane type = " +planetype)
	
	//Store the number of engines----------------------------------------------------
	
	if(document.calculator.engine[0].checked) {
		engine = 1;
	}
	
	if(document.calculator.engine[1].checked) {
		engine = 2;
	}
	
	//alert("Engine number = " +engine);
	
	//Calculate plane and engine product------------------------------------------
	
	if (planetype == "narrowone" && engine == 1) {
		enginetaxi = 2.4;
	}
	
	if (planetype == "narrowtwo" && engine == 1) {
		enginetaxi = 3.9;
	}
	
	if (planetype == "wideone" && engine == 1) {
		enginetaxi = 4.8;
	}
	
	if (planetype == "widetwo" && engine == 1) {
		enginetaxi = 6;
	}
	
	if (planetype == "widethree" && engine == 1) {
		enginetaxi = 9.6;
	}
	
	if (planetype == "narrowone" && engine == 2) {
		enginetaxi = 4;
	}
	
	if (planetype == "narrowtwo" && engine == 2) {
		enginetaxi = 6.5;
	}
	
	if (planetype == "wideone" && engine == 2) {
		enginetaxi = 8;
	}
	
	if (planetype == "widetwo" && engine == 2) {
		enginetaxi = 10;
	}
	
	if (planetype == "widethree" && engine == 2) {
		enginetaxi = 16;
	}
	
	//alert("Aircraft classification x 1 or 2 engine taxi = " +enginetaxi);
	
	
	//Store the daily arrivals------------------------------------------
	
	dailyarrivals = document.getElementById('arrivals').value;
	
	if (!dailyarrivals) { //Error check
		alert("Please insert a value for daily arrivals");
	}
	
	if (dailyarrivals < 0) {
		alert("Please insert a value greater than 0 for daily arrivals");
		return;
	}
	
	//Store the reduced time---------------------------------------------------
	
	reducedtime = document.getElementById('taxitime').value;
	//alert("Reduced Time = " +reducedtime);
	
	
	//Annual fuel savings algorithm--------------------------------------------------
	
	monetaryvalue = enginetaxi * dailyarrivals * avgfuelprice * reducedtime * daysinyear;
	
	if (currency == "euro") {
		monetaryvalue = parseFloat(monetaryvalue)*0.748839;
		
		//Change unit that gets printed
		document.getElementById("monetaryunit").innerHTML = "Euro / Year";
		document.getElementById("euroselect").style.color = "#FFFFFF";
		document.getElementById('dollarselect').style.color = "#3c3c3d";
	} else {
		document.getElementById("monetaryunit").innerHTML = "USD / Year";
		document.getElementById('euroselect').style.color = "#3c3c3d";
		document.getElementById('dollarselect').style.color = "#FFFFFF";
	}
	
	//Reduced emissions algorithm--------------------------------------------------
	
	emissionsvalue = (enginetaxi * dailyarrivals * reducedtime * daysinyear * emissionsrate);

	
	//Print the result on submit--------------------------------------------------------------
	if (currency == "euro") {
		document.getElementById("monetaryvalue").innerHTML = "&euro;"+comma(monetaryvalue.toFixed(0));
	} else {
		document.getElementById("monetaryvalue").innerHTML = "$"+comma(monetaryvalue.toFixed(0));
	}
	
	document.getElementById("emissionsvalue").innerHTML = comma(emissionsvalue.toFixed(0));
}

function comma(nStr) {
	nStr += '';
	x = nStr.split('.');
	x1 = x[0];
	x2 = x.length > 1 ? '.' + x[1] : '';
	var rgx = /(\d+)(\d{3})/;
	while (rgx.test(x1)) {
		x1 = x1.replace(rgx, '$1' + ',' + '$2');
	}
	return x1 + x2;
}

function disablereturn(evt) {
	var evt  = (evt) ? evt : ((event) ? event : null);

	var node = (evt.target) ? evt.target : ((evt.srcElement) ? evt.srcElement : null);

	if ((evt.keyCode == 13) && (node.type=="text")) {return false;}
}

document.onkeypress = disablereturn;