function coverage(tabId) 
    {
		document.getElementById('tab_1').style.display = "none";
		document.getElementById('tab_2').style.display = "none";
		document.getElementById('tab_3').style.display = "none";
		
		if (tabId == 1)
			{
				document.getElementById('tab_1').style.display = "block";
			}
		if (tabId == 2)
			{
				document.getElementById('tab_2').style.display = "block";
			}
		if (tabId == 3)
			{
				document.getElementById('tab_3').style.display = "block";
			}			
		
	}