// JavaScript Document
function calculateCarbonEmission(f)
{
	var fields = Array(
			Array(	'electricity', 1	),
			Array(	'unleadedPetrol', 2.6	),
			Array(	'lpg', 1.8	),
			Array(	'diesel', 3	),
			Array(	'airKms', 0.18	)
		);
	var totalCarbon = 0, carbon = 0, ele = null;
	
	for ( key in fields ) {
		ele = document.getElementById(fields[key][0]);
		
		if (ele && ele.value) {
			carbon = Math.round(parseFloat(ele.value) * fields[key][1] / 10)/100;
			totalCarbon += carbon;
			
			ele = document.getElementById(fields[key][0]+'Carbon');
			ele.innerHTML = carbon;
			
			ele = document.getElementById(fields[key][0]+'Offset');
			if (ele) {
				ele.innerHTML = ('$'+(carbon * 25).toFixed(2));
			}
		}
	}
	ele = document.getElementById('totalCarbon');
	ele.innerHTML = totalCarbon.toFixed(3) + ' tonnes';

	ele = document.getElementById('totalOffset');
	if (ele) {
		ele.innerHTML = '$'+(totalCarbon*25).toFixed(2);
	}
	if (document.offset && document.offset.hidden) {
		document.offset.hidden.value = totalCarbon;
	}
	return false;
}