var currentUnits = "UK";

	function three()
	{
		var kcomp = document.getElementById('kform')['comp[]'];
		var kayaks_num = 0;

		for(i=0; i < kcomp.length; i++)
		{
			if(kcomp[i] && kcomp[i].checked)
			{
				kayaks_num++;
			}
		}
		if(kayaks_num > 3)
			alert('you may compare up to three kayaks at a time');
		return kayaks_num;
	}
	
	function submitKayaks()
	{
		var k = three();
		if(k<=0 || k >3 )
		{
			if(k<=0)
				alert('please choose one, two or three kyaks to compare');
		}
		else
			document.getElementById("kform").submit();
		
	}

	function changeKayakUnits()
	{
		if(currentUnits == "UK")
		{
			document.getElementById("UK").style.display = 'none';
			document.getElementById("US").style.display = 'block';
			document.getElementById("unitButton").innerHTML = 'change to UK units';
			currentUnits = "US";
		}
		else
		{
			document.getElementById("US").style.display = 'none';
			document.getElementById("UK").style.display = 'block';
			document.getElementById("unitButton").innerHTML = 'change to US units';
			currentUnits = "UK";
		}
	}
	
	
	function changeCompareUnits()
	{
		if(currentUnits == "UK")
		{
			document.getElementById("compare_uk").style.display = 'none';
			document.getElementById("compare_us").style.display = 'block';
			document.getElementById("unitButton").innerHTML = 'change to UK units';
			currentUnits = "US";
		}
		else
		{
			document.getElementById("compare_us").style.display = 'none';
			document.getElementById("compare_uk").style.display = 'block';
			document.getElementById("unitButton").innerHTML = 'change to US units';
			currentUnits = "UK";
		}
	}