//1 U.S. GALLON=  	128 OUNCES
//1 Imp Gallon = 160 Imp Ounces
//1 imperial gallon = 134.555785 fluid ounces
// 1 LITER=  	33.815 FLUID OUNCES
//1000 ml == 33.815 oz
// 1 oz (US)  = 29.5727 ml  
// 1 oz (Imp)  = 28.41307 ml  
//29.57267485
//www.rccanada.ca Gas Calculator

function calculate(){
	var alertFlag = false;
	var errorMessage = "";
	if(document.calc_form.gas_quantity.value == "-1"){
		errorMessage += "Please select gas quantity."+"\n";
		alertFlag = true;
	}
	if(document.calc_form.ratio.value == "-1"){
		errorMessage += "Please select oil mix ratio."+"\n";
		alertFlag = true;
	}	
	if(alertFlag){
		alert(errorMessage);
	}else{
		var numGallons = document.calc_form.gas_quantity.value;
		var mixRatio = document.calc_form.ratio.value;
		var numOunces = document.calc_form.gas_quantity.value * 153.7217;  //US onces in Imp Gallon
		var numOuncesImp = document.calc_form.gas_quantity.value * 160;  //Imp oz in Imp Gallon
		
		var oilQuantityOZ = numOunces/mixRatio;
		var oilQuantityOZImp = numOuncesImp/mixRatio;
		var oilQuantityML = (oilQuantityOZ * 29.574);
		document.calc_form.result_oz.value = roundOff(oilQuantityOZ, 2);
		document.calc_form.result_oz_imp.value = roundOff(oilQuantityOZImp, 2);
		document.calc_form.result_ml.value = roundOff(oilQuantityML, 2);
	}
}
function roundOff(value, precision){
        value = "" + value //convert value to string
        precision = parseInt(precision);
        var whole = "" + Math.round(value * Math.pow(10, precision));
        var decPoint = whole.length - precision;
        if(decPoint != 0){
                result = whole.substring(0, decPoint);
                result += ".";
                result += whole.substring(decPoint, whole.length);
        }else{
                result = whole/(Math.pow(10, precision));
        }
        return result;
}
function clearAll(){
	document.calc_form.result_oz.value  = "";
	document.calc_form.result_oz_imp.value  = "";
	document.calc_form.result_ml.value  = "";
}