function calculateROI() {
	
	showROIloader();
	
	var lpd = $('loads_per_day').value;
	var ds = $('duration_shuttle').value;
	var spd = $('shifts_per_day').value;
	var hs = $('hours_per_shift').value;
	var dlc = $('duration_load_conv').value;
	var duc = $('duration_unload_conv').value;
	var costs_per_year_fte = $('costs_per_year_fte').value;
	
	if( strlen(lpd) > 0 && 
	    strlen(ds) > 0 && 
	    strlen(spd) > 0 && 
	    strlen(hs) > 0 && 
	    strlen(dlc) > 0 && 
	    strlen(duc) > 0 &&
	    strlen(costs_per_year_fte) > 0) {
		
		var params = 'lpd=' + lpd;
			params += '&ds=' + ds;
			params += '&spd=' + spd;
			params += '&hs=' + hs;
			params += '&dlc=' + dlc;
			params += '&duc=' + duc;
			params += '&costs_per_year_fte=' + costs_per_year_fte;
		
		var completeHandler = function(t) {
			var response = t.responseText;
			
			if(response != "failed") {
				
				var params = response.split(":");
				
				$('roi_result_in_years').innerHTML = params[0];
				$('roi_result_in_months').innerHTML = params[1];
				
				new Effect.Fade("roi_start", { 
					duration: 0.5,
					afterFinish: function() {
						
						new Effect.Appear("roi_result", { 
							duration: 0.5,
							afterFinish: function() {
								
								hideROIloader();
							}
						});
					}
				});
			}
			else {
				
				hideROIloader();
				
				$('loads_per_day').focus();
				
				alert('Please fill in correct ROI numbers!');
			}
		}
		
		new Ajax.Request("/special/ajax/roi_calculation.php", {
			asynchronous: true, method: 'post', 
			parameters: params, onComplete: completeHandler
		});
	}
	else {
		
		hideROIloader();
		
		$('loads_per_day').focus();
		
		alert('Please fill in correct ROI numbers!');
	}
}

function showROIloader() {
	
	new Effect.Appear("roi_loader", {
		duration: 0.3,
		from: 0.0,
		to: 0.8
	});
}

function hideROIloader() {
	
	new Effect.Fade("roi_loader", {
		duration: 0.3,
		from: 0.8,
		to: 0.0
	});
}