var currentParameter = "NO3";
        if (document.images)
        {
                var NO3image = new Image(120,20);
                NO3image.src =
			"images/NO3button.png";
                var NO3selimage = new Image(120,20);
                NO3selimage.src =
			"images/NO3selbutton.png";
                var NH4image = new Image(120,20);
                NH4image.src =
			"images/NH4button.png";
                var NH4selimage = new Image(120,20);
                NH4selimage.src =
			"images/NH4selbutton.png";
                var PO4image = new Image(120,20);
                PO4image.src =
			"images/PO4button.png";
                var PO4selimage = new Image(120,20);
                PO4selimage.src =
			"images/PO4selbutton.png";
                var NO2image = new Image(120,20);
                NO2image.src =
			"images/NO2button.png";
                var NO2selimage = new Image(120,20);
                NO2selimage.src =
			"images/NO2selbutton.png";
                var Siimage = new Image(120,20);
                Siimage.src =
			"images/Sibutton.png";
                var Siselimage = new Image(120,20);
                Siselimage.src =
			"images/Siselbutton.png";
	}

function setParameter(newParameter)
{
	if (newParameter == currentParameter) return;
	if (currentParameter == "NO3")
	{
		document.images["NO3image"].src =
			NO3image.src;
	}
	if (currentParameter == "NH4")
	{
		document.images["NH4image"].src =
			NH4image.src;
	}
	if (currentParameter == "PO4")
	{
		document.images["PO4image"].src =
			PO4image.src;
	}
	if (currentParameter == "NO2")
	{
		document.images["NO2image"].src =
			NO2image.src;
	}
	if (currentParameter == "Si")
	{
		document.images["Siimage"].src =
			Siimage.src;
	}
	if (newParameter == "NO3")
	{
		document.images["NO3image"].src =
			NO3selimage.src;
	}
	if (newParameter == "NH4")
	{
		document.images["NH4image"].src =
			NH4selimage.src;
	}
	if (newParameter == "PO4")
	{
		document.images["PO4image"].src =
			PO4selimage.src;
	}
	if (newParameter == "NO2")
	{
		document.images["NO2image"].src =
			NO2selimage.src;
	}
	if (newParameter == "Si")
	{
		document.images["Siimage"].src =
			Siselimage.src;
	}
	currentParameter = newParameter;
}