function refreshCharts() {
	
	var chartPeriod = document.getElementById('chartPeriod').value;	
	refreshChart(document.getElementById('combinedChart'), chartPeriod);
	
}

function refreshChart(chart, newPeriod) {
	
	var oldUrl = chart.src;
	var chartPeriodArgName = 'chartPeriod=';
	
	var end = oldUrl.indexOf(chartPeriodArgName) + chartPeriodArgName.length;
	var newUrl = oldUrl.substring(0, end) + newPeriod;
	
	chart.src = newUrl;
	
}