window.addEvent('domready', function(){
	var form = $('frmMain');
	var cfp = $('currentfuelprice');
	var bfp = $('basefuelprice');
	var mpg = $('averagemilespergallon');
	var fsr = $('fuelsurchargerate');

	var format = function(el){
		value = parseFloat(el.value)
		el.value = isNaN(value) ? '0' : value;
	}
	
	var calculate = function(){
		var milespergallon = parseFloat(mpg.value);
		fsr.value = (isNaN(milespergallon) || milespergallon == '0') ? 'Invalid Miles per Gallon' : ((cfp.value - bfp.value) / mpg.value).toFixed(2);
		return false;
	}

	form.addEvent('submit', calculate);
	cfp.addEvent('blur', format.pass(cfp));
	bfp.addEvent('blur', format.pass(bfp));
	mpg.addEvent('blur', format.pass(mpg));
});