function fuelcalculation()
        {
        var error_flag = false;
        var error_string = "";
        if (isNaN(document.calcfuel.mileage.value))
                {
                error_flag = true
                error_string = error_string + "Non numeric mileage.\n"
                }
        else
                {
                if (document.calcfuel.mileage.value < 100)
                        {
                        error_flag = true
                        error_string = error_string + "Mileage very low.\n"
                        }
                }

        if (isNaN(document.calcfuel.increase.value))
                {
                error_flag = true
                error_string = error_string + "Non numeric price increase.\n"
                }

        if (isNaN(document.calcfuel.mpg.value))
                {
                error_flag = true
                error_string = error_string + "Non numeric miles per gallon.\n"
                }
        else
                {
                if (document.calcfuel.mpg.value < 5)
                        {
                        error_flag = true
                        error_string = error_string + "MPG very low.\n"
                        }
                else
                        if (document.calcfuel.mpg.value >200)
                                {
                                error_flag = true
                                error_string = error_string + "Nice car with a high MPG.\n"
                                }
                }

        if (isNaN(document.calcfuel.cost.value))
                {
                error_flag = true
                error_string = error_string + "Non numeric fuel price.\n"
                }
        else
                {
                if (document.calcfuel.cost.value < 20 || document.calcfuel.cost.value > 200)
                        {
                        error_flag = true
                        error_string = error_string + "Fuel price is very cheap.\n"
                        }
                }

        if (error_flag)
                alert(error_string);
        else
                {
                var litres = ((document.calcfuel.mileage.value / document.calcfuel.mpg.value) * 4.5461);
                var currentcost = (parseInt((litres * document.calcfuel.cost.value) / 100));
		var plusone = (parseFloat(parseFloat(document.calcfuel.increase.value) + parseFloat(document.calcfuel.cost.value)));
		var tax = (parseInt((litres * 0.471) + (currentcost * 0.175)));		
                var newcost = (parseInt((litres * plusone) / 100));
                var difference = (newcost - currentcost);
                error_string = "At these prices you spend £" + currentcost + " a year on road fuel, £" + tax + " of this is RAW TAX.\nIf your fuel increased " + document.calcfuel.increase.value +" p per litre, your fuel bill would go up to £" + newcost + "\nA stagering increase of £" + difference +" a year.\n";
                alert(error_string);
                }
        }