// asAtDate must be a string of type yyyymmdd
	// function returns price, or -1 if out of range
	function getHistoricalIANGPrice(asAtDate)
	{
		var count = wlIANGDateArr.length;
		var date = parseInt(asAtDate);
		if (date > wlIANGDateArr[count-1] || date < wlIANGDateArr[0])
			return -1;
		
		var lower = 0;
		var upper = count-1;
		var index = parseInt(upper/2);
		var curDate;

		// binary search for date
		while(upper - lower > 1)
		{
			curDate = wlIANGDateArr[index];
			if (curDate == date)
				return wlIANGPriceArr[index];
			if (curDate > date)
				upper = index;
			else
				lower = index;
			index = parseInt((upper+lower)/2);
		}
		// Make sure that what we've found is actually the right day.
		if (wlIANGDateArr[lower] == date) {
			return wlIANGPriceArr[lower];
		} 
		else if(wlIANGDateArr[count-1] == date)
		{
		    return wlIANGPriceArr[count-1];
		}
		else {
			return -1;
		}
	}
	
    function showHistoricalIANGPrice() {
		var f = document.forms.HistoricalIANGDataForm;
		var d = ("00" + f.day.value).slice(-2);
		var m = ("00" + f.month.value).slice(-2);
		var y = ("0000" + f.year.value).slice(-4);

		if (isNaN(parseInt(d))
			|| isNaN(parseInt(m))
			|| isNaN(parseInt(y))) {

			alert("Please enter a date in dd/mm/yyyy format");
			return;
		}

		var price = parseFloat(getHistoricalIANGPrice(y + m + d))
		if (price.toFixed != null) { price = price.toFixed(2); }
		var msg = "On " + d + "/" + m + "/" + y + " the price was $" + price;

		if (price > -1) {
			alert(msg);
		} else {
			alert("No price information on that date");
		}
	}