function show_minus()
	{
	ch1a.style.display="none";
	ch1b.style.display="block";
	ch2a.style.display="none";
	ch2b.style.display="block";
	ch3a.style.display="none";
	ch3b.style.display="block";
	ch4a.style.display="none";
	ch4b.style.display="block";
	ch5a.style.display="none";
	ch5b.style.display="block";
	ch6a.style.display="none";
	ch6b.style.display="block";
	ch7a.style.display="none";
	ch7b.style.display="block";
	}
	function show_plus()
	{
	ch1a.style.display="block";
	ch1b.style.display="none";
	ch2a.style.display="block";
	ch2b.style.display="none";
	ch3a.style.display="block";
	ch3b.style.display="none";
	ch4a.style.display="block";
	ch4b.style.display="none";
	ch5a.style.display="block";
	ch5b.style.display="none";
	ch6a.style.display="block";
	ch6b.style.display="none";
	ch7a.style.display="block";
	ch7b.style.display="none";
	}
	function show_ch1b()
	{
	ch1a.style.display="none";
	ch1b.style.display="block";
	}
	function show_ch1a()
	{
	ch1a.style.display="block";
	ch1b.style.display="none";
	}
	function show_ch2b()
	{
	ch2a.style.display="none";
	ch2b.style.display="block";
	}
	function show_ch2a()
	{
	ch2a.style.display="block";
	ch2b.style.display="none";
	}
	function show_ch3b()
	{
	ch3a.style.display="none";
	ch3b.style.display="block";
	}
	function show_ch3a()
	{
	ch3a.style.display="block";
	ch3b.style.display="none";
	}
	function show_ch4b()
	{
	ch4a.style.display="none";
	ch4b.style.display="block";
	}
	function show_ch4a()
	{
	ch4a.style.display="block";
	ch4b.style.display="none";
	}
	function show_ch5b()
	{
	ch5a.style.display="none";
	ch5b.style.display="block";
	}
	function show_ch5a()
	{
	ch5a.style.display="block";
	ch5b.style.display="none";
	}
	function show_ch6b()
	{
	ch6a.style.display="none";
	ch6b.style.display="block";
	}
	function show_ch6a()
	{
	ch6a.style.display="block";
	ch6b.style.display="none";
	}

	function show_ch7b()
	{
	ch7a.style.display="none";
	ch7b.style.display="block";
	}
	function show_ch7a()
	{
	ch7a.style.display="block";
	ch7b.style.display="none";
	}