function Calculation()
	{
	var error_flag = false;
	var error_string = "";
	
	if (isNaN(document.fuel_calc.entered_miles.value))
		{
		error_flag = true
		error_string = error_string + "Non numeric entered_miles.\n"
		}
	
	if (isNaN(document.fuel_calc.entered_mpg.value))
		{
		error_flag = true
		error_string = error_string + "Non numeric miles per gallon.\n"
		}
		
	if (isNaN(document.fuel_calc.entered_fuel.value))
		{
		error_flag = true
		error_string = error_string + "Non numeric fuel price.\n"
		}
		
	if (error_flag)
		alert(error_string);
	else
		{
		var fuelcost = ((document.fuel_calc.entered_miles.value / document.fuel_calc.entered_mpg.value) * 4.54 * document.fuel_calc.entered_fuel.value) / 100;
		fuelcost = (parseInt(fuelcost * 100)) / 100;
		
		if (isNaN(fuelcost))
			{
			error_string = "Incorrect data entered\n";
			alert(error_string);
			}
		else
			{
			document.fuel_calc.result_expenditure.value=fuelcost;
			return false;
			}
		}
	}