Sum Help

[toolman]

Hi,

 

I have this script which adds up various options in some drop down menus. However, if I select/keeps selecting an option, it add it to the total each time I select it. Is there a way I can have it so it it only adds it on once and to use an either/or method - so only one value will be added?

 

var sum =499;
var count=0;
var output;
function UpdateCost()
{

   var i = document.getElementById('graphic');


	    sum = sum + parseFloat(document.getElementById('graphic').value);

	    document.getElementById('result').value = sum;


}
function UpdateCost2()
{

   var i = document.getElementById('transit');

	    sum = sum + parseFloat(document.getElementById('transit').value) ;

	    document.getElementById('result').value = sum;

}

function UpdateCost3()
{

   var i = document.getElementById('lights');

	    sum = sum + parseFloat(document.getElementById('lights').value) ;

	    document.getElementById('result').value = sum;

}
function UpdateCost4()
{

   var i = document.getElementById('wooden');

	    sum = sum + parseFloat(document.getElementById('wooden').value) ;

	    document.getElementById('result').value = sum;

}
function UpdateCost5()
{

   var i = document.getElementById('case');

	    sum = sum + parseFloat(document.getElementById('case').value) ;

	    document.getElementById('result').value = sum;

}

 

Thanks!